U.S. patent application number 10/730950 was filed with the patent office on 2004-06-24 for illumination apparatus and camera.
Invention is credited to Tenmyo, Yoshiharu.
Application Number | 20040120135 10/730950 |
Document ID | / |
Family ID | 32588174 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040120135 |
Kind Code |
A1 |
Tenmyo, Yoshiharu |
June 24, 2004 |
Illumination apparatus and camera
Abstract
An illumination apparatus is disclosed, whose aperture portion
can be made smaller while achieving miniaturization of the
apparatus and higher condensing efficiency. The illumination
apparatus comprising a light source, and a condensing unit that
condenses light emitted from the light source toward the optical
axis, wherein the condensing unit includes a negative lens portion
that is arranged on a front side of the apparatus and has negative
refractive power, a positive lens portion that is arranged near the
optical axis and has positive refractive power, and a reflection
portion that reflects emitted light that is not directed to the
positive lens portion toward the optical axis.
Inventors: |
Tenmyo, Yoshiharu;
(Kanagawa, JP) |
Correspondence
Address: |
ROBIN BLECKER & DALEY
2ND FLOOR
330 MADISON AVENUE
NEW YORK
NY
10017
US
|
Family ID: |
32588174 |
Appl. No.: |
10/730950 |
Filed: |
December 9, 2003 |
Current U.S.
Class: |
362/16 |
Current CPC
Class: |
G03B 2215/0535 20130101;
G03B 2215/0525 20130101; G03B 2215/0532 20130101; G03B 15/05
20130101 |
Class at
Publication: |
362/016 |
International
Class: |
G03B 015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2002 |
JP |
362780/2002 |
Claims
What is claimed is:
1. An illumination apparatus comprising: a light source; and a
condensing unit that condenses light emitted from the light source
toward the optical axis; wherein the condensing unit includes a
negative lens portion that is arranged on a front side of the
apparatus and has negative refractive power, a positive lens
portion that is arranged near the optical axis and has positive
refractive power, and a reflection portion that reflects emitted
light that is not directed to the positive lens portion toward the
optical axis.
2. The illumination apparatus according to claim 1, wherein the
condensing unit is configured such that it condenses the light
emitted from the light source to a predetermined focus point; and
wherein the negative lens portion is positioned closer to the light
source than the focus point.
3. The illumination apparatus according to claim 1, wherein
negative lens portion is shaped such that its length in the
vertical direction of the apparatus is smaller than a maximum
length of the condensing unit in the vertical direction of the
apparatus.
4. The illumination apparatus according to claim 3, wherein the
negative lens portion and the condensing unit are formed such that
the following expression is
satisfied:0.4.ltoreq.D/A.ltoreq.0.8wherein D is the maximum length
of negative lens portion in the vertical direction of the
apparatus, and A is the maximum length of the condensing unit in
the vertical direction of the apparatus.
5. The illumination apparatus according to claim 1, wherein the
negative lens portion and the condensing unit are formed such that
the following expression is
satisfied:0.1.ltoreq.L/B.ltoreq.0.5wherein L is the distance in
optical axis direction between a maximum aperture position of the
negative lens and a maximum aperture position of the condensing
lens, and B is the distance in optical axis direction between a
maximum aperture position of the condensing unit and the light
source center.
6. The illumination apparatus according to claim 1, comprising an
optical member including the positive lens portion, the reflection
portion and the negative lens portion.
7. The illumination apparatus according to claim 1, comprising: a
first optical member including the positive lens portion and the
reflection portion; and a second optical member including the
negative lens portion.
8. The illumination apparatus according to claim 7, wherein an
optical irradiation angle can be changed by changing the distance
between the first optical member and the second optical member.
9. The illumination apparatus according to claim 1, wherein the
reflection portion comprises a total reflection surface configured
as a mirror surface.
10. The illumination apparatus according to claim 1, wherein the
negative lens portion is made of a lens having a concave continuous
surface or of a cylindrical lens.
11. The illumination apparatus according to claim 1, further
comprising a reflection screen that is arranged to the rear of the
apparatus behind the light source and reflects light emitted from
the light source to the front of the apparatus; wherein the
reflection screen has a curved surface that is substantially
concentric to the light source center.
12. The illumination apparatus according to claim 1, wherein the
light source is a straight tube-shaped flashlight discharge tube
extending in width direction of the apparatus.
13. A camera comprising an illumination apparatus according to
claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to illumination apparatuses as
well as cameras equipped with an illumination apparatus, and in
particular to illumination apparatuses, in which the length, in
vertical direction of the apparatus, of the outgoing aperture
portion through which light is emitted from the illumination
apparatus is shortened without making the overall shape of the
apparatus larger.
[0003] 2. Description of Related Art
[0004] Illumination apparatuses used for cameras and the like are
conventionally configured with a light source and an optical
component such as a reflective mirror or Fresnel lens that guides
the light rays emitted from the light source to the front of the
apparatus (i.e. toward the object).
[0005] Regarding such illumination apparatuses, there have been
various proposals for condensing the light rays that are emitted
from the light source into various directions with high efficiency
to the necessary illumination range. In particular in recent years,
apparatuses have been proposed with which an improvement of the
condensing efficiency as well as a miniaturization of the apparatus
can be attained by placing an optical member utilizing total
reflection, such as a prism light guide, instead of a Fresnel lens
that is placed at the front of the apparatus with respect to the
light source.
[0006] As one such apparatus, Japanese Patent Application Laid-Open
No. H4 (1992)-138438 (referred to as "Document 1" in the following)
discloses an illumination optical system that condenses light rays
emitted from a light source to the front of the apparatus with a
lens having positive refractive power, while directing the light
rays that have been emitted from the light source toward the side
of the apparatus to the front of the apparatus and condensing them
by a total-reflection surface at which they are reflected, thereby
irradiating illumination light from the same outgoing surface. That
is to say, there are illumination optical systems using a prism
making it possible to achieve miniaturization and increase the
condensing efficiency, in which those of the light rays that are
emitted from the light source whose optical path has been divided
at an ingoing surface position of an optical member are emitted
from the same outgoing surface,
[0007] As an improvement of this illumination optical system,
Japanese Patent Application Laid-Open No. H8 (1996)-262537
(referred to as "Document 2" in the following) proposes an
apparatus in which miniaturization of the entire illumination
optical system is achieved by placing the prism in front of the
light source in the apparatus, and in which the surface of the
prism that emits the totally reflected light is tilted with respect
to the optical axis.
[0008] On the other hand, in illumination apparatuses of the type
in which the irradiation angle range of the illumination light is
fixed, in the tele state in which the necessary irradiation angle
range is narrow as the image-taking optical system has been zoomed
to a high zoom ratio, illumination light is irradiated onto an
unnecessary range, which leads to a large energy loss. In order to
address this problem and to eradicate the energy loss, several
illumination apparatuses with variable irradiation angle have been
proposed, with which the irradiation angle range of the
illumination light can be changed in accordance with a change of
the image-taking range (zooming of the image-taking optical
system).
[0009] In one such illumination apparatus, the irradiation angle
range of the illumination light is changed by moving a first
optical member and a second optical member to change the spacing
between them. More specifically, as disclosed in Japanese Patent
Application Laid-Open No. 2000-298244 (referred to as "Document 3"
in the following), the first optical member converts light rays
emitted from the light source to the front of the apparatus into
light rays of an optical axis direction, and includes a convex lens
serving as a portion of the ingoing surface, a total reflection
surface that converts light rays emitted from the light source to
the side of the apparatus by total reflection into light rays of
the optical axis direction, and an outgoing surface made of a
plurality of small lenses.
[0010] The second optical member includes, on an ingoing surface
onto which the light emitted from the first optical member is
incident, a plurality of lenses that cancel the refractive power of
the small lenses of the first optical member. Moreover, the
irradiation angle range of the illumination light can be changed by
moving the above-described first optical member and the second
optical member relative to one another.
[0011] In recent years, as camera bodies become smaller, there is a
need for making illumination optical systems that are mounted on
the camera body and serves as an auxiliary light source even
smaller. To address this, Documents 1 and 2 etc. propose
illumination optical systems that strive for miniaturization and
higher performance by using prisms of the above-described
types.
[0012] On the other hand, in order to adapt to new camera designs,
there is a strong demand for further improvements of these
illumination optical systems, and in particular for a smaller
aperture portion (in the vertical direction of the camera) serving
as the light emission region that is apparent from the outside of
the product (camera). That is to say, there is a demand for making
only the aperture portion of the illumination apparatus smaller,
while making the illumination apparatus smaller by using prisms as
in the conventional technology, which is a very difficult demand
that could not be realized with the prior art.
[0013] In the illumination optical systems of both Document 1 and
Document 2, the portion where the total reflection surface is
broadest serves as the opening (aperture) of the illumination
optical system, and making the aperture portion smaller was not
possible by a mere extension of the conventional approach without
severely lowering the optical characteristics (light distribution
characteristics).
[0014] Moreover, the demand to make the aperture portion of the
illumination apparatus smaller is not restricted to the
above-described illumination apparatuses in which the irradiation
angle range of the illumination light is fixed, and the same demand
is also strong for illumination apparatuses in which the
irradiation angle range can be changed.
[0015] However, as can be understood from the illumination
apparatus of the light-guide type disclosed in Document 3, the size
of the aperture portion in conventional illumination apparatuses of
the type with variable irradiation angle needs to be approximately
the same size as the aperture portion (outgoing surface of the
first optical member) that is formed by the portion where the total
reflection surface is broadest, and the aperture portion of the
illumination apparatus cannot be said to be sufficiently small.
Also most of the other illumination apparatuses of the type with
variable irradiation angle, the aperture portion of the
illumination apparatus (optical member) needs to be much broader
than the reflection screen for condensing, and by a mere extension
of the conventional approach, a further miniaturization of the
aperture portion is not possible without considerably lowering the
optical characteristics.
SUMMARY OF THE INVENTION
[0016] It is thus the primary object of the present invention to
provide an illumination apparatus, whose aperture portion can be
made smaller while achieving miniaturization of the apparatus and
higher condensing efficiency by using an optical member (prism). It
is also an object of the present invention to provide an
illumination apparatus with which uniform light distribution
characteristics can be maintained on the irradiation surface,
efficiently using the energy from the light source.
[0017] An illumination apparatus according to one aspect of the
present invention includes a light source, comprising a light
source, and a condensing unit that condenses light emitted from the
light source toward the optical axis, wherein the condensing unit
includes a negative lens portion that is arranged on a front side
of the apparatus and has negative refractive power, a positive lens
portion that is arranged near the optical axis and has positive
refractive power, and a reflection portion that reflects emitted
light that is not directed to the positive lens portion toward the
optical axis.
[0018] A camera according to one aspect of the present invention
includes such an illumination apparatus.
[0019] These and further objects and features of the scanning
display optical system of the present invention will become
apparent from the following detailed description of preferred
embodiments thereof taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a cross-sectional view through the center of a
flashlight emitting apparatus according to Embodiment 1 of the
present invention, taken along the radial direction of the
flashlight discharge tube.
[0021] FIG. 2 is a diagram showing the distribution of light rays
from the light source in Embodiment 1 of the present invention.
[0022] FIG. 3 is a diagram showing the distribution of light rays
from the light source in Embodiment 1 of the present invention.
[0023] FIG. 4 is a cross-sectional view of a flashlight emitting
apparatus according to Embodiment 1 of the present invention, taken
along the longitudinal direction of the flashlight discharge
tube.
[0024] FIG. 5 is an exploded perspective view showing the structure
of the essential components of the flashlight emitting apparatus
according to Embodiment 1 of the present invention.
[0025] FIG. 6 is an external perspective view of a camera equipped
with the flashlight emitting apparatus according to Embodiment 1 of
the present invention.
[0026] FIG. 7 is a cross-sectional view of a flashlight emitting
apparatus according to Embodiment 2 of the present invention, taken
along the radial direction of the flashlight discharge tube.
[0027] FIG. 8 is a diagram illustrating the concept behind the
shape of the condensing optical system in Embodiment 2 of the
present invention.
[0028] FIG. 9 is a diagram showing the distribution of light rays
from the light source in Embodiment 2 of the present invention.
[0029] FIG. 10 is a diagram showing the distribution of light rays
from the light source in Embodiment 2 of the present invention.
[0030] FIG. 11 is a cross-sectional view of a flashlight emitting
apparatus according to Embodiment 2 of the present invention, taken
along the longitudinal direction of the flashlight discharge
tube.
[0031] FIG. 12 is an exploded perspective view showing the
structure of the essential components of the flashlight emitting
apparatus according to Embodiment 2 of the present invention.
[0032] FIG. 13 is a cross-sectional view of a flashlight emitting
apparatus according to Embodiment 3 of the present invention, taken
along the radial direction of the flashlight discharge tube
(condensing state).
[0033] FIG. 14 is a cross-sectional view of a flashlight emitting
apparatus according to Embodiment 3 of the present invention, taken
along the radial direction of the flashlight discharge tube
(divergent state).
[0034] FIG. 15 is a diagram showing the distribution of light rays
from the light source in Embodiment 3 of the present invention
(condensing state).
[0035] FIG. 16 is a diagram showing the distribution of light rays
from the light source in Embodiment 3 of the present invention
(divergent state).
[0036] FIG. 17 is a diagram illustrating the concept behind the
shape of the condensing optical system according to Embodiment 3 of
the present invention.
[0037] FIG. 18 is a cross-sectional view of a flashlight emitting
apparatus according to Embodiment 3 of the present invention, taken
along the longitudinal direction of the flashlight discharge
tube.
[0038] FIG. 19 is an exploded perspective view showing the
structure of the essential components of the flashlight emitting
apparatus according to Embodiment 3 of the present invention.
[0039] FIG. 20 is a cross-sectional view of a flashlight emitting
apparatus according to Embodiment 4 of the present invention, taken
along the radial direction of the flashlight discharge tube
(condensing state).
[0040] FIG. 21 is a cross-sectional view of a flashlight emitting
apparatus according to Embodiment 4 of the present invention, taken
along the radial direction of the flashlight discharge tube
(divergent state).
[0041] FIG. 22 is a diagram illustrating the concept behind the
shape of the condensing optical system in Embodiment 4 of the
present invention.
[0042] FIG. 23 is a diagram showing the distribution of light rays
from the light source in Embodiment 4 of the present invention
(condensing state).
[0043] FIG. 24 is a diagram showing the distribution of light rays
from the light source in Embodiment 4 of the present invention
(divergent state).
[0044] FIG. 25 is a cross-sectional view of a flashlight emitting
apparatus according to Embodiment 4 of the present invention, taken
along the longitudinal direction of the flashlight discharge
tube.
[0045] FIG. 26 is an exploded perspective view showing the
structure of the essential components of the flashlight emitting
apparatus according to Embodiment 4 of the present invention.
[0046] FIG. 27 is a diagram illustrating the concept behind the
shape of the condensing optical system according to Embodiment 5 of
the present invention.
[0047] FIG. 28 is a diagram showing the distribution of light rays
from the light source in Embodiment 5 of the present invention
(condensing state).
[0048] FIG. 29 is a diagram showing the distribution of light rays
from the light source in Embodiment 5 of the present invention
(divergent state).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] The following is a detailed description of embodiments of
the present invention, with reference to the accompanying
drawings.
[0050] Embodiment 1
[0051] Referring to the accompanying drawings, the following is a
description of an illumination apparatus according to Embodiment 1
of the present invention. FIGS. 1 to 6 are drawings illustrating
the illumination apparatus of this embodiment, in particular a
flashlight emitting apparatus. The flashlight emitting apparatus of
this embodiment is of the type with fixed illumination angle.
[0052] FIG. 1 is a cross-sectional view of the flashlight emitting
apparatus, along the radial direction of the flashlight discharge
tube. FIGS. 2 and 3 are diagrams in which ray tracing of the light
emitted from the light source center has been added to the
cross-sectional view of FIG. 1. FIG. 4 is a cross-sectional view of
a flashlight emitting apparatus along the longitudinal direction of
the flashlight discharge tube. Moreover, FIG. 5 is an exploded
perspective view showing the structure of the essential components
of the flashlight emitting apparatus, and FIG. 6 is an external
perspective view of a camera equipped with the flashlight emitting
apparatus.
[0053] In FIG. 6, numeral 1 denotes an optical prism arranged
inside the flashlight emitting apparatus, which converts, in the
manner described below, light rays emitted from the light source
into light rays having a predetermined angular range. Numeral 21
indicates a release button. Pressing this release button 21 half
down initiates an image-taking preparation operation (focus
adjustment operation and light metering operation etc.), and
pressing it down entirely initiates an image-taking operation
(exposure of film or exposure of an image pickup element, such as a
CCD, and recording of image data that have been read from the image
pickup element onto a recording medium). Numeral 22 denotes a power
source switch of the camera, and numeral 23 denotes a window
portion that is arranged at the camera front in a finder optical
system through which the object is observed.
[0054] Numeral 24 denotes a window portion of a light metering
device that measures the brightness of external light. Numeral 25
denotes a lens barrel provided with an image-taking lens, allowing
zooming of the image-taking optical system by advancing and
retracting in the direction of the image-taking optical axis.
Numeral 26 denotes a camera body, in which the necessary components
for image-taking are arranged. It should be noted that the function
of the other of the above-mentioned components besides the
flashlight emitting apparatus are as known in the art, so that a
further detailed explanation thereof has been omitted. Also, there
is no limitation to the above-described structure of the components
in the camera of this embodiment.
[0055] FIG. 5 is an exploded perspective view illustrating the
internal structure of a flashlight emitting apparatus of a camera
as shown in FIG. 6. It should be noted that this drawing shows only
the essential components of the flashlight emitting apparatus, and
holding members and lead wires are not depicted.
[0056] In FIG. 5, an optical prism 1, which is made of a glass
material or optical resin material with high transmittivity such as
acrylic resin, is arranged on the emission side (to the front of
the apparatus) in the flashlight emitting apparatus. Numeral 2
denotes a straight tube-shaped flashlight discharge tube (xenon
tube) that emits flashlight when a trigger signal is input into it.
Numeral 3 denotes a reflection screen that reflects to the front of
the apparatus those components of the light rays emitted from the
flashlight discharge tube 2 that have been emitted to the rear of
the apparatus. The inner side (reflection surface) of this
reflection screen 3 is made of a metallic material having high
reflectivity, such as brilliance aluminum or the like.
[0057] In the structure of above described camera, the following is
a description of the camera operation for this structure, when the
camera has been set to the "strobe auto-mode," for example.
[0058] When the user pushes the release button 21 half down, the
brightness of the external light is measured by the light metering
device, and the result of the light measurement is sent to a
central processing unit arranged inside the camera body 26.
Depending on the brightness of the external light and the
sensitivity of the imaging medium (film or image pickup element,
such as a CCD), the central processing unit judges whether the
flashlight emitting apparatus should emit light or not.
[0059] If it is judged that the flashlight emitting apparatus
should emit light, then, by giving out a light emission signal to
the flashlight emitting apparatus when the release button 21 is
pushed completely down, the central processing unit lets the
flashlight discharge tube emit light via a trigger lead wire (not
shown in the drawings) that is attached to the reflection screen 3.
Here, those light rays emitted from the flashlight discharge tube 2
that are emitted in the direction opposite from the illumination
direction (direction of an object side) are reflected by the
reflection screen 3 arranged at the rear of the apparatus and are
guided in the illumination direction. Moreover, the light rays that
are emitted in the illumination direction are directly incident on
the optical prism 1 arranged at the front of the apparatus, and
after being converted to predetermined light distribution
characteristics, they are irradiated onto the object.
[0060] With the flashlight emitting apparatus of the present
embodiment, the size (in vertical direction of the camera) of the
outgoing aperture portion of the flashlight emitting apparatus that
can be seen in the external appearance of the camera can be made
small, as explained below, and the light distribution
characteristics can be optimized. Referring to FIGS. 1 to 3, the
following is a more detailed description of a method for setting
the optimum shape of the flashlight emitting apparatus (optical
prism).
[0061] FIGS. 1 to 3 are vertical cross-sectional views of the
flashlight emitting apparatus, taken along the radial direction of
the flashlight discharge tube 2. In these drawings, numeral 1
denotes the optical prism for controlling the light distribution,
numeral 2 denotes the straight tube-shaped flashlight discharge
tube, numeral 3 denotes the reflection screen, which has a
semi-circular tube portion 3a that is concentric to the flashlight
discharge tube 2, and numeral 4 denotes a cover serving as an outer
member of the camera body 26.
[0062] In addition to the cross section of FIG. 1, FIGS. 2 and 3
also show the tracing of representative light rays emitted from the
inner center of the flashlight discharge tube 2. Here, FIG. 2 is a
ray tracing diagram of those components of the light rays emitted
from the flashlight discharge tube 2 that are close to the emission
optical axis (referred to as "optical axis" in the following). FIG.
3 is a ray tracing diagram of those components of the light rays
emitted from the flashlight discharge tube 2 that are emitted in a
direction away from the optical axis (i.e. up or down in FIG. 3).
It should be noted that apart from the light rays in FIGS. 2 and 3,
the structure and shape of the entire illumination optical system
are the same.
[0063] The flashlight emitting apparatus of this embodiment is
characterized in that the size of the outgoing aperture portion of
the flashlight emitting apparatus in the vertical direction of the
apparatus (aperture height) can be minimized while maintaining the
light distribution characteristics in the vertical direction of the
apparatus uniform. In the following, the characteristic features of
the shape of the flashlight emitting apparatus (optical prism 1)
and the behavior of the light rays emitted from the flashlight
discharge tube 2 are explained in detail.
[0064] First, the behavior of the light rays in an actual
illumination optical system is described in detail using the ray
tracing diagram shown in FIGS. 2 and 3. FIG. 2 shows the inner and
outer diameter of a glass tube serving as the flashlight discharge
tube 2. As for the light-emitting phenomenon of the flashlight
discharge tube 2, it can be assumed that, in order to improve the
light emission efficiency, light emission is mostly caused at the
entire inner diameter of the flashlight discharge tube 2, and light
emission is substantially uniform at the entire inner diameter of
the flashlight discharge tube 2.
[0065] On the other hand, at the design stage, in order to
efficiently control the light that is emitted from the flashlight
discharge tube 2 serving as the light source, it is preferable to
design the shape of the illumination optical system under the
assumption that there is an ideal point light source at the light
source center, rather than simultaneously taking into account all
light rays of the entire inner diameter of the flashlight discharge
tube 2. Then, efficient design is possible if, after the shape of
the illumination optical system has been designed, a correction is
performed in consideration of the fact that the light source has a
finite size. Also this embodiment follows this approach, and the
center of the light source is taken as the reference when
determining the shape of the illumination optical system, and the
shape of all the parts in the illumination optical system is set as
described below.
[0066] The ray tracing diagram shown in FIG. 2 shows those
components of the light rays emitted from the light source center
that are emitted directly toward the ingoing surface 1a of the
optical prism 1. These components form a relatively small angle
with respect to the optical axis, and are subjected only to the
refraction by the optical prism 1.
[0067] The ingoing surface (positive lens portion) 1a of the
optical prism 1 is made of a cylindrical lens having positive
refractive power, and has a very large refractive power. Therefore,
the light rays that are emitted from the light source center and
that pass through the ingoing surface 1a are condensed toward the
optical axis, as shown in FIG. 2. After these light rays have been
converted to a predetermined light distribution by refraction at
the outgoing surface 1b of the optical prism 1, they are emitted
toward the object.
[0068] The outgoing surface (negative lens portion) 1b of the
optical prism 1 is made of a cylindrical lens having negative
refractive power, and the light rays that are condensed toward the
optical axis by the ingoing surface la are refracted by the
outgoing surface 1b and directed in a direction away from the
optical axis. Thus, the irradiation angle range of the light rays
that have passed through the outgoing surface 1b is broadened.
[0069] In this manner, those light rays emitted from the light
source center that are directly incident on the ingoing surface la
are emitted near the optical axis at a narrow region (central
region) of the outgoing surface 1b of the optical prism 1 that is
narrower than the ingoing surface 1a, and converted into light rays
having an angular range that is narrower than the angular range
when emitted from the light source.
[0070] On the other hand, those light rays emitted from the light
source center that travel towards the rear of the apparatus are
reflected by the reflection screen 3 that is arranged at the rear
of the apparatus. Here, the reflection screen 3 has a semi-circular
tube portion 3a that is concentric to the light source center, so
that the light rays that are reflected by the semi-circular tube
portion 3a are guided back to the vicinity of the light source
center. After that, they are emitted from the central region in the
outgoing surface 1b of the optical prism 1, taking the same optical
path as described above.
[0071] Here, the important point is that the region through which
the light rays emitted from the light source center pass at the
outgoing surface 1b is narrower than the region through which they
pass at the ingoing surface 1a, and the angular region of the light
rays emitted from the outgoing surface 1b is narrower than the
angular region when they are incident on the ingoing surface 1a.
That is to say, when the light source is considered to be a point
light source, then, by forming an ingoing surface 1a having strong
positive refractive power at the ingoing surface side of the
optical prism 1 and forming.an outgoing surface 1b having negative
refractive power at the outgoing side, the light rays emitted from
the light source center are first condensed by the ingoing surface
1a toward the optical axis and then emitted from a region of the
outgoing surface 1b with a relatively smooth curvature near the
optical axis. Thus, it is possible to emit efficiently condensed
light rays from a narrow region of the outgoing surface 1b.
[0072] On the other hand, the ray tracing diagram shown in FIG. 3
shows those components of the light rays emitted from the light
source center that are incident on the ingoing surfaces 1c and 1c'
of the optical prism 1. That is to say, the light rays shown in
FIG. 3 correspond to those components that form a larger angle with
the optical axis than the light rays shown in FIG. 2, and are
reflected at the optical prism 1.
[0073] Here, the ingoing surfaces 1c and 1c' of the optical prism 1
are made of surfaces forming a relatively large angle with the
optical axis. Thus, the light rays incident on the ingoing surfaces
1c and 1c' are refracted by the ingoing surfaces 1c and 1c' and
guided to the total reflection surfaces (reflective portions) 1d
and 1d'. Then, the light rays reflected at the total reflection
surfaces 1d and 1d' are condensed toward the optical axis.
[0074] As mentioned above, the ingoing surfaces 1c and 1c' are
configured as surfaces forming a relatively large angle with the
optical axis, because, if the inclination angle of the ingoing
surfaces 1c and 1c' with respect to the optical axis were small,
then some components of the light rays emitted from the light
source center would undergo total reflection at the ingoing
surfaces 1c and 1c', and the light rays emitted from the light
source would be directed in a direction that is different from the
intended direction of the ray tracing shown in FIG. 3. Thus, the
present embodiment represses the occurrence of components that are
totally reflected by the ingoing surfaces 1c and 1c', by providing
the ingoing surfaces 1c and 1c' with a predetermined
inclination.
[0075] The components reflected by the total reflection surfaces 1d
and 1d' are guided to a region of the outgoing surface 1b that is
narrower than the region of the ingoing surfaces 1c and 1c', as
shown by the ray tracing diagram in FIG. 3. At the same time, the
components that have been reflected by the total reflection
surfaces 1d and 1d' are guided to peripheral regions at the upper
and the lower edge of the outgoing surface 1b, and a large angular
change is attained due to the refraction at this region when those
components are emitted from the optical prism 1. And moreover, the
angle of inclination of the light rays emitted from the outgoing
surface 1b with respect to the optical axis becomes small.
Moreover, the angular range of the light rays emitted from the
optical prism 1 is considerably narrower than the angular range of
light rays before incidence on the optical prism 1.
[0076] On the other hand, components of light rays emitted from the
light source center and directed toward the rear of the apparatus
that form relatively large angle with the optical axis are
reflected by the reflection screen 3 arranged at the rear of the
apparatus. Here, the reflection screen 3 has a semi-circular tube
portion 3a that is concentric to the light source center, so that
the light rays reflected by the semi-circular tube portion 3a of
the reflection screen 3 are guided to near the light source center.
After that, they are emitted from the peripheral regions of the
outgoing surface 1b of the optical prism 1, taking the same optical
path as described above.
[0077] Thus, as becomes clear from the ray tracing diagrams of the
two components as shown in FIGS. 2 and 3, in both cases, the
regions through which the light passes at the outgoing surface 1b
is narrower than the region of the ingoing surfaces 1a and 1c
(1c'), and the irradiation angle range is made extremely narrow by
the irradiation into and emission out of the optical prism 1.
Therefore, a superior condensing effect is attained, with a narrow
outgoing aperture portion (outgoing surface 1b).
[0078] Moreover, light rays traveling through the refractive
optical path as shown in FIG. 2 or the total reflection optical
path as shown in FIG. 3 both pass through the outgoing surface 1b,
and this outgoing surface 1b is made of a continuously curved
surface, so that the influence of discrepancies due to machining
precision of each part or positional shifts when assembling the
illumination optical system can be reduced. That is to say, even
when the position of the light rays that reach the outgoing surface
1b is slightly shifted, this hardly affects the optical
characteristics, and consistent optical characteristics can be
attained.
[0079] With the above-described structure of the illumination
optical system, considerable changes in the optical characteristics
also tend not to occur in the case that the size of the light
source is assumed to have a certain constant size, and continuous
changes in the optical characteristics are attained with respect to
changes in the size of the light source, so that this structure is
advantageous for providing illumination optical systems with a
uniform light distribution.
[0080] Here, the outgoing surface 1b of the optical prism 1 is not
made of a complicated surface, but of a single concave surface, so
that there is the advantage that it can also be used directly as an
external component of the flashlight emitting apparatus.
Furthermore, in the flashlight emitting apparatus of the present
embodiment, the light emitted from the light source can be
condensed with very few structural components, so that there are
the advantages that the condensing efficiency is high, and a
uniform illumination without irregularities in the light
distribution is attained with regard to the optical
characteristics.
[0081] With the flashlight emitting apparatus of this embodiment,
in the illumination optical system using the optical prism 1, it is
possible to make only the size of the outgoing aperture portion
(outgoing surface 1b) of the flashlight emitting apparatus smaller
with respect to the vertical direction of the apparatus, while
taking advantage of the characteristic features of small size and
high condensing efficiency. That is to say, the size (apparatus
height) that is necessary for the illumination optical system
depends on the size given by the total reflection surfaces 1d and
1d', but the size of the outgoing aperture portion that is actually
necessarily in order to irradiate illumination light onto the
object can be made much smaller than the size constituted by the
total reflection surfaces 1d and 1d'.
[0082] An ideal shape of the illumination optical system according
to the present embodiment is described with reference to FIG. 1.
FIG. 1 is a cross-sectional view of a flashlight emitting apparatus
taken along the radial direction of the flashlight discharge tube
2. FIG. 1 shows the positional relation between a cover 4 serving
as an outer member of the camera body 26 and the illumination
optical system. As explained above, it is the outgoing surface 1b
of the optical prism 1 that functions as the outgoing aperture
portion of the illumination optical system, so that the cover 4 is
formed such that only the outgoing surface 1b is exposed to the
outside of the camera. Thus, the size, with respect to the vertical
direction of the apparatus, of the aperture portion formed in the
cover 4 can be made small, and the characteristic features of the
illumination optical system of the present embodiment can be
utilized best.
[0083] Moreover, the tip portions 1h of the optical prism 1 that
are formed on the light source side are configured such that they
extend to a position corresponding to the light source center, as
shown in FIG. 1. The reason for this is that if the tip portions 1h
of the optical prism 1 were positioned further to the front of the
apparatus than a position corresponding to the light source center,
then those components of the light rays emitted from the light
source that are emitted at an angle of substantially 90.degree. to
the optical axis (i.e. upward or downward in FIG. 1) cannot be
picked up, and the light rays emitted from the light source cannot
be condensed efficiently.
[0084] If, on the other hand, the tip portions 1h of the optical
prism 1 were formed such that they extend to the rear of the
apparatus behind the position corresponding to the light source
center so as to try to gather efficiently all of the light emitted
from the light source, then the optical prism 1 would become large.
And moreover, it would become difficult to totally reflect the
light rays emitted from the light source at the reflection surfaces
1d and 1d', and the components leaking from the optical prism 1
would increase, so that the light rays emitted from the light
source cannot be utilized efficiently.
[0085] For this reason, with regard to the condensing efficiency
and size of the illumination optical system, it is preferable that
the tip portions 1h of the optical prism 1 are formed to a position
that substantially matches the position of the light source center,
as shown in FIG. 1.
[0086] As mentioned above, the reflection screen 3 has a
semi-circular tube portion 3a that is concentric to the light
source center, and at both ends of the semi-circular tube portion
3a, there are lateral portions 3b that are formed in one piece with
the semi-circular portion 3a, and that are bent to the rear side of
the apparatus with respect to the tip portions 1h of the optical
prism 1.
[0087] As shown in the ray tracing diagrams in FIGS. 2 and 3, the
light rays emitted from the light source center do not leak from
the total reflection surfaces 1d and 1d' of the optical prism 1,
but within the light rays emitted from a position that is slightly
off the center of the light source, there are light rays that leak
from the total reflection surfaces 1d and 1d'. For this reason, by
providing the reflection screen 3 with the lateral portions 3b, the
light rays leaked from the total reflection surfaces 1d and 1d'
reflect at the lateral portions 3b, and are incident again on the
total reflection surfaces 1d and 1d' of the optical prism 1.
[0088] As shown in FIG. 1, the lateral portions 3b of the
reflection screen 3 are formed along the total reflection surfaces
1d and 1d' of the optical prism 1, so that also the light that is
reflected at the lateral portions 3b and incident again at the
total reflection surfaces 1d and 1d' can be effectively utilized as
object illumination light.
[0089] The following is an explanation of the ideal shape of the
optical prism 1. First, the dimensions of the optical prism 1 in
the vertical direction of the apparatus are explained.
[0090] In FIG. 1, it is preferable that the aperture height D of
the outgoing surface 1b in the vertical direction of the apparatus
is within the range of the Expression (1). That is, the ratio
between the aperture height D of the outgoing surface 1b of the
optical prism 1 and the maximum height A constituted by the total
reflection surfaces 1d and 1d' of the optical prism is given
by:
0.4.ltoreq.D/A.ltoreq.0.8 (1)
[0091] In order to adapt to new camera designs, it would be ideal
to suppress the aperture height D as much as possible, but
depending on the size of the flashlight discharge tube 2 serving as
the light source, the light loss becomes larger as the length of
the aperture height D is shortened, and it may not be possible to
configure an effective condensing optical system.
[0092] That is to say, if the aperture height D of the outgoing
surface 1b is shortened, and the size of the light source is
increased, the light that travels directly to the outgoing surface
1b of the optical prism 1 is reduced, and the components that
repeatedly undergo total reflection inside the optical prism 1 are
increased. As a result, most of the components that would have been
emitted from the outgoing surface 1b are emitted from other
portions of the optical prism 1, and those components of the light
rays emitted from the light source that can be used effectively for
the illumination of the object are decreased. Consequently, with
the above structure, even though the aperture height D of the
outgoing surface 1b is reduced, it is still not necessarily an
ideal illumination optical system with regard to the effective
utilization of light rays emitted from the light source.
[0093] With regard to this, the lower limit of Expression (1) is
the aperture height D of the outgoing surface 1b that functions
effectively as the illumination optical system if the size
(diameter) of the flashlight discharge tube 2 serving as the light
source is relatively small. And the upper limit of Expression (1)
becomes the aperture height D that functions effectively for the
illumination optical system if the size (diameter) of the
flashlight discharge tube 2 is large.
[0094] Thus, if the diameter of the flashlight discharge tube 2 is
small, the lower limit of Expression (1) is the size of the
aperture height D that functions effectively for the illumination
optical system, and it follows from the expression that the
aperture height D can be made smaller if the flashlight discharge
tube 2 is made smaller. However, due to such reasons as the
durability and the manufacturing process of the actual flashlight
discharge tube 2, there are no flashlight discharge tubes 2 below a
certain diameter.
[0095] Considering the diameter of flashlight discharge tubes 2
that can be manufactured in practice, then a lower limit for D/A of
0.4 seems appropriate.
[0096] On the other hand, if the upper limit 0.8 for D/A in
Expression (1) is exceeded, then the aperture height D becomes
large, which is not desirable with regard to the object of the
present invention, namely to reduce the size of the outgoing
aperture portion in the vertical direction of the apparatus.
[0097] The following is a discussion of actual numbers for
Expression (1) in a flashlight emitting apparatus according to the
present embodiment. In the present embodiment, the diameter (inner
diameter) of the flashlight discharge tube 2 is .phi.1.3 mm, the
maximum height A of the total reflection surfaces 1d and 1d' of the
optical prism 1 is 5 mm, and the aperture height D of the outgoing
surface 1b of the optical prism 1 is 3 mm. From these numbers, it
follows that the value of D/A in Expression (1) is 0.6, which is
approximately the median of Expression (1).
[0098] It is preferable that the shape of the optical prism 1 of
the present embodiment in the optical axis direction is as follows:
When L is the distance from the tips of the outgoing surface 1b to
the maximally outer contour (maximum aperture position) of the
total reflection surfaces 1d and 1d', and B is the distance from
the maximally outer contour of the total reflection surfaces 1d and
1d' to the light source center, then the ratio L/B is in the
following range:
0.1.ltoreq.L/B.ltoreq.0.5 (2)
[0099] In Expression (2), considering miniaturization of the
flashlight emitting apparatus in the optical axis direction, it is
preferable that the distance L is as short as possible. However, in
order to form the outgoing surface 1b, a certain length is
necessary for manufacturing reasons for example. Moreover, a
certain length L is necessary in order to configure the cover 4
serving as the outer member of the camera body 26 such that it
follows the outer lateral surfaces 1i of the outgoing surface 1b,
to make the outgoing surface 1b of the optical prism 1 appear
smaller.
[0100] In the present embodiment, considering these two aspects,
the relation of the distance L and the distance B is set such that
the Expression (2) is satisfied.
[0101] The lower limit 0.1 in Expression (2) is set based on the
distance L and the distance B that are necessary to form the
optical prism 1 in view of those two aspects. If the lower limit is
undercut, then it is not possible to configure an illumination
optical system that is effective with regard to condensing
efficiency and the like.
[0102] On the other hand, the upper limit of 0.5 in Expression (2)
is set based on the following viewpoint: If L/B is greater than
0.5, then the length of the optical prism 1 in the optical axis
direction is increased (i.e. becomes larger), and the original
goal, namely to make the flashlight emitting apparatus smaller,
which is one effect of this embodiment, is missed.
[0103] The following is a discussion of actual numbers for
Expression (2) in a flashlight emitting apparatus according to the
present embodiment. In the present embodiment, the distance L is
1.1 mm and the distance B is 3.9 mm. From these numbers, it follows
that L/B is 0.28, which is approximately the median of Expression
(2).
[0104] Thus, by restricting the shape of the optical prism 1 to the
ranges given in the Expressions (1) and (2), the optical prism 1
can be kept from becoming larger, and the aperture height D of the
outgoing surface 1b can be reduced.
[0105] Referring to FIG. 4, the following is an explanation of the
structure of the flashlight emitting apparatus with regard to the
axial direction of the flashlight discharge tube 2. FIG. 4 is a
cross-sectional view of a flashlight emitting apparatus taken along
the axial direction (longitudinal direction) of the flashlight
discharge tube 2, and the same numerals are given to members
corresponding to those explained for FIGS. 1 to 3.
[0106] A characteristic feature of the optical prism 1 is that the
lateral sides positioned at its two ends are provided with total
reflection surfaces 1e and 1e'. Thus, the light rays that deviate
from the range that is necessary for irradiating illumination light
onto the object (necessary irradiation angle range) undergo total
reflection at the total reflection surfaces 1e and 1e', and can be
guided to within the necessary irradiation angle range, and the
light rays emitted from the light source can be effectively
utilized.
[0107] Another characteristic feature of the shape of the outgoing
surface 1b of the optical prism 1 is that the end faces located at
both ends in longitudinal direction of the outgoing surface 1b are
slanted surfaces 1f and 1f'. Thus, it can be repressed that light
rays that are emitted from the light source and that are directed
within the necessary irradiation angle range escape at the two ends
of the outgoing surface 1b, and the distractive sensation at the
seam to the cover 4 serving as the outer member of the camera body
26 can be eliminated.
[0108] On the other hand, by forming a cylindrical lens with
negative refractive power over the entire central region of the
outgoing surface 1b, a structure is attained in which the
condensing effect in the vertical direction of the apparatus is not
adversely affected. Moreover, by making the central region of the
outgoing surface 1b of a cylindrical lens with a single convex
surface, there is the advantage that the camera can be provided
with a clear-cut appearance without distracting features.
[0109] In this embodiment, an example of an illumination optical
system was shown with a structure in which the light rays emitted
from the light source center are broadened through an optical prism
1 to a necessary irradiation angle range. However, the present
invention is not limited to the form of the optical prism 1 in the
above-described Embodiment 1.
[0110] For example, it is also possible to configure the convex
cylindrical lens forming the ingoing surface of the optical prism
with a Fresnel lens having positive refractive power, and to
configure the concave cylindrical lens forming the outgoing surface
with a Fresnel lens having negative refractive power. Moreover, in
the present embodiment, the reflective surfaces 1d and 1d' of the
optical prism 1 are formed as total reflection surfaces, and they
may be made of metal deposition surfaces, in which case the limit
of the angle of light rays incident on the reflective surfaces
becomes small, so that the optical prism can be made smaller and
the light rays emitted from the light source can be condensed more
efficiently.
[0111] Moreover, in the present embodiment, the reflective screen 3
is made of a semi-circular tube portion 3a that is concentric to
the center of the flashlight emitting tube 2, but there is no
limitation to this shape, and it is also possible to form the
reflective screen such that it has a curved surface of the second
order.
[0112] Embodiment 2
[0113] FIGS. 7 to 12 illustrate a flashlight emitting apparatus
(illumination apparatus) according to Embodiment 2 of the present
invention. It should be noted that the flashlight emitting
apparatus of this embodiment is of the type with fixed illumination
angle.
[0114] FIG. 7 is a cross-sectional view of the flashlight emitting
apparatus, along the radial direction of the flashlight discharge
tube, and FIG. 8 illustrates the concept behind the shape of the
optical prism. FIGS. 9 and 10 are diagrams in which ray tracing of
the light emitted from the light source center has been added to
the cross-sectional view of FIG. 7. FIG. 11 is a cross-sectional
view of a flashlight emitting apparatus along the axial direction
(longitudinal direction) of the flashlight discharge tube, and FIG.
12 is an exploded perspective view showing the structure of the
essential components of the flashlight emitting apparatus.
[0115] FIG. 12, which is an exploded perspective view illustrating
the internal structure of the flashlight emitting apparatus, shows
the essential portions of the flashlight emitting apparatus, but
does not show holding members or lead wires.
[0116] In FIG. 12, numeral 6 denotes an optical prism that is made
of a glass material or optical resin material with high
transmittivity such as acrylic resin, and that is arranged on the
emission side (to the front of the apparatus) in the flashlight
emitting apparatus. Numeral 7 denotes a tube-shaped flashlight
discharge tube (xenon tube) that emits flashlight when a trigger
signal is input into it. Numeral 8 denotes a reflection screen that
reflects to the emission side (to the front of the apparatus) those
components of the light rays emitted from the flashlight discharge
tube 7 that have been emitted to the rear of the apparatus. The
inner side (reflection surface) of this reflection screen 8 is made
of a metallic material having high reflectivity, such as brilliance
aluminum or the like. It should be noted that the flashlight
emitting apparatus of this embodiment is provided in a camera as
described in Embodiment 1 (FIG. 6).
[0117] The main aspects of the flashlight emitting apparatus of
this embodiment are that the size of the outgoing aperture portion
of the flashlight emitting apparatus that can be seen from outside
the camera (i.e. the size in the vertical direction of the camera)
is decreased, and the light rays emitted from the flashlight
discharge tube are optimally condensed. Referring to FIGS. 7 to 11,
the following is a detailed description of a method for setting the
most suitable shape of the flashlight emitting apparatus (optical
prism).
[0118] FIGS. 7 to 10 are longitudinal cross-sectional views of the
flashlight emitting apparatus along a radial direction of the
flashlight discharge tube. In these drawings, numeral 6 denotes an
optical prism for controlling light distribution, numeral 7 denotes
a tube-shaped flashlight discharge tube, numeral 8 denotes a
reflection screen having a semi-circular tube portion 8a that is
concentric to the flashlight discharge tube 7, and numeral 9
denotes a cover serving as an outer member of the camera body.
[0119] In addition to the cross section view of FIG. 7, FIGS. 8 to
10 also show the tracing of representative light rays emitted from
a radially central portion (light source center) of the flashlight
discharge tube 7. Here, FIG. 9 is a ray tracing diagram of those
components of the light rays emitted from the flashlight discharge
tube 7 that are close to the emission optical axis (referred to as
"optical axis" in the following). FIG. 10 is a ray tracing diagram
of those components of the light rays emitted from the flashlight
discharge tube 7 that are emitted in a direction away from the
optical axis (i.e. up or down in FIG. 10). It should be noted that
apart from the light rays in FIGS. 8 to 10, the structure and shape
of the entire illumination optical system is the same.
[0120] The flashlight emitting apparatus of this embodiment is
characterized in that the shape of the illumination optical system
is determined such that the light emitted from the flashlight
emitting apparatus is condensed optimally while minimizing the size
of the outgoing aperture portion of the flashlight emitting
apparatus in the vertical direction of apparatus (aperture height).
In the following, the characteristic features of the shape of the
optical prism 6 and the behavior of the light rays emitted from the
flashlight discharge tube 7 are explained in detail.
[0121] First, the approach that was taken to determine the shape of
the illumination optical system in this embodiment is explained in
detail with reference to the ray tracing diagrams (FIGS. 8 to 10)
of the actual illumination optical system.
[0122] FIG. 8 is a drawing showing the behavior of the light rays
emitted from the light source center after they have been incident
the optical prism 6. A characteristic feature of this embodiment is
that the illumination optical system is configured such that a
plurality of light rays emitted from the light source center reach
predetermined positions that are continuously arranged on the
outgoing surface 6b of the optical prism 6, without crossing or
interfering with one another. That is to say, the shape of the
optical prism 6 is determined such that each of a plurality of
angles at which the light rays that are emitted from the light
source center corresponds to a specific location on the outgoing
surface 6b.
[0123] Moreover, assuming that the optical prism 6 is sufficiently
long in the optical axis direction, the shape of the various parts
of the optical prism 6 is determined such that the light rays
emitted from the light source are condensed on substantially one
point (focus point) O, as shown by the broken lines in FIG. 8.
[0124] By determining the shape of the various portions of the
optical prism 6 (ingoing surfaces 6a, 6c and 6c', total reflection
surfaces 6d and 6d', and outgoing surface 6b) in this manner, the
aperture height of the outgoing surface (outgoing surface 6b) of
the illumination optical system can be reduced to a minimum.
Moreover, by configuring the outgoing surface 6b of the optical
prism 6 with a lens having a suitable negative refractive power, it
becomes possible to appropriately adjust the irradiation angle
range. Thus, an efficient condensing optical system that has a
small outgoing aperture portion, in accordance with the object of
the present invention, can be configured.
[0125] Regarding the shape of the outgoing surface 6b of the
optical prism 6, the present embodiment strives for an illumination
optical system with the best condensing properties, and the shape
of the outgoing surface 6b is determined as described below with
reference to FIGS. 9 and 10.
[0126] The ray tracing diagram shown in FIG. 9 shows those
components of the light rays emitted from the light source center
that are directly incident on the ingoing surface 6a of the optical
prism 6. These light components form an angle with the optical axis
that is relatively small, and are only subjected to the refraction
by the optical prism 6.
[0127] The ingoing surface (positive lens portion) 6a of the
optical prism 6 is made of a cylindrical lens having positive
refractive power, and has a very strong refractive power, so that
the light rays that are emitted from the light source center and
pass through the ingoing surface 6a' are condensed toward the
optical axis, as shown in FIG. 9. After these light rays have been
refracted. at the outgoing surface 6b of the optical prism 6 and
converted into light rays that are parallel to the optical axis,
they are emitted in the direction toward the object.
[0128] Here, the outgoing surface (negative lens portion) 6b of the
optical prism 6 is made of a cylindrical lens having negative
refractive power, and the light rays that have been condensed
toward the optical axis by the ingoing surface 6a are turned into
light rays that are parallel to the optical axis, due to the
refraction of the outgoing surface 6b.
[0129] Those of the light rays emitted from the light source center
that are incident on the ingoing surface 6a are emitted from a
region (central region) of the outgoing surface 6b of the optical
prism 6 near the optical axis that is narrower than the ingoing
surface 6a, and are converted into light rays that have an angular
distribution that is much narrower than the irradiation angles when
emitted from the light source.
[0130] On the other hand, those of the light rays emitted from the
light source center that are directed toward the rear of the
apparatus are reflected by the reflection screen 8 arranged at the
rear of the apparatus. Here, the reflection screen 8 has a
semi-circular tube portion 8a that is concentric to the light
source center, so that the light rays that are reflected by the
semi-circular tube portion 8a of the reflection screen 8 are guided
back to the vicinity of the light source center. After that, they
are emitted from the central region in the outgoing surface 6b of
the optical prism 6, taking the same optical path as described
above.
[0131] Here, the important point is that the region through which
the light rays emitted from the light source center pass at the
outgoing surface 6b is narrower than the region through which they
pass at the ingoing surface 6a, and the angular region of the light
rays emitted from the outgoing surface 6b is narrower than the
angular region when they are incident on the ingoing surface 6a.
That is to say, when the light source is considered to be a point
light source, then, by forming an ingoing surface 6a having strong
positive refractive power at the ingoing side of the optical prism
6 and forming an outgoing surface 6b having negative refractive
power at the outgoing side, the light rays emitted from the light
source center are first condensed by the ingoing surface 1a toward
the optical axis and then emitted from a region of the outgoing
surface 6b with a relatively smooth curvature near the optical
axis. Thus, it is possible to emit efficiently condensed light rays
from a narrow region of the outgoing surface 6b.
[0132] On the other hand, the ray tracing diagram shown in FIG. 10
shows those components of the light rays emitted from the light
source center that are incident on the ingoing surfaces 6c and 6c'
of the optical prism 6. That is to say, the light rays shown in
FIG. 10 correspond to those components that form a larger angle
with the optical axis than the light rays shown in FIG. 9, and are
reflected at the optical prism 6.
[0133] Here, the ingoing surfaces 6c and 6c' of the optical prism 6
are made of surfaces forming a relatively large angle with the
optical axis. Thus, as in Embodiment 1, the light rays incident on
the ingoing surfaces 6c and 6c' are refracted by the ingoing
surfaces 6c and 6c' and guided to the total reflection surfaces
(reflective portions) 6d and 6d. Then, the light rays reflected at
the total reflection surfaces 6d and 6d' are condensed toward the
optical axis.
[0134] The ingoing surfaces 6c and 6c' are made of surfaces forming
a relatively large angle with the optical axis, because, if the
inclination angle of the ingoing surfaces 1c and 1c'0 with respect
to the optical axis were small, then some components of the light
rays emitted from the light source center would undergo total
reflection at the ingoing surfaces 6c and 6c', and the light rays
emitted from the light source would be directed in a direction that
is different from the intended direction of the ray tracing shown
in FIG. 10. Thus, as in Embodiment 1, the present embodiment
represses the occurrence of components that are totally reflected
by the ingoing surfaces 6c and 6c', by providing the ingoing
surfaces 6c and 6c' with a predetermined inclination.
[0135] The components reflected by the total reflection surfaces 6d
and 6d' are guided to a region of the outgoing surface 6b that is
narrower than the regions of the ingoing surfaces 6c and 6c', as
shown by the ray tracing diagram in FIG. 10. At the same time, the
components that have been reflected by the total reflection
surfaces 6d and 6d' are guided, continuously and without crossing,
to peripheral regions at the upper and the lower edge of the
outgoing surface 6b, and are converted into light rays that are
parallel to the optical axis, due to the refraction at those
regions. Thus, the angular range of the light rays emitted from the
optical prism 6 (outgoing surface 6b) is considerably narrower than
the angular range of light rays before incidence on the optical
prism 6 (ingoing surfaces 6c and 6c').
[0136] On the other hand, components of light rays emitted from the
light source center and directed toward the rear of the apparatus
that form relatively large angle with the optical axis are
reflected by the reflection screen 8 arranged at the rear of the
apparatus. Here, the reflection screen 8 has a semi-circular tube
portion 8a that is concentric to the light source center, so that
the light rays reflected by the semi-circular tube portion 8a of
the reflection screen 8 are guided to near the light source center.
After that, they are emitted from the peripheral regions in the
outgoing surface 6b of the optical prism 6, taking the same optical
path as described above.
[0137] Thus, as becomes clear from the ray tracing diagrams of the
two components as shown in FIGS. 9 and 10, in both cases, the
regions through which the light passes at the outgoing surface 6b
is narrower than the regions of the ingoing surfaces 6a and 6c
(6c'). Moreover, the light rays emitted from the light source
center are all converted into light rays that are parallel to the
optical axis. Therefore, a favorable condensing effect is attained,
with a narrow outgoing aperture portion (outgoing surface 6b).
[0138] Moreover, light rays traveling through the refractive
optical path as shown in FIG. 9 and the total reflection optical
path as shown in FIG. 10 both pass through the outgoing surface 6b,
and this outgoing surface 6b is made of a continuously curved
surface, so that the influence of discrepancies due to machining
precision of each part or positional shifts when assembling the
illumination optical system can be reduced. That is to say, even
when the position of the light rays that reach the outgoing surface
6b is slightly shifted, this hardly affects the optical
characteristics, and consistent optical characteristics can be
attained.
[0139] With the above-described structure of the illumination
optical system, considerable changes in the optical characteristics
also tend not to occur in the case that the size of the light
source has a certain constant size, and continuous changes in the
optical characteristics are attained with respect to changes in the
size of the light source, so that this structure is advantageous
for providing illumination optical systems with a uniform light
distribution.
[0140] Here, even though its central region is sunk down deeper
than that of the outgoing surface 1b of the optical prism 1 in
Embodiment 1, the outgoing surface 6b of the optical prism 6 is not
made of a complicated surface, but of a single concave surface, so
that there is the advantage that it can also be used directly as an
external component of the flashlight emitting apparatus.
Furthermore, in the flashlight emitting apparatus of the present
embodiment, the light emitted from the light source can be
condensed with very few structural components, so that the
condensing efficiency is high, and a uniform illumination without
irregularities in the light distribution is attained with regard to
the optical characteristics.
[0141] With the flashlight emitting apparatus of this embodiment,
in the illumination optical system using the optical prism 6, it is
possible to make only the size of the outgoing aperture portion
(outgoing surface 6b) of the flashlight emitting apparatus smaller
in the vertical direction of the apparatus, while taking advantage
of the characteristic features of small size and high condensing
efficiency. That is to say, the size (apparatus height) that is
necessary for the illumination optical system depends on the size
given by the total reflection surfaces 6d and 6d', but the size of
the outgoing aperture portion that is actually necessarily in order
to irradiate illumination light onto the object can be made much
smaller than the size constituted by the total reflection surfaces
6d and 6d'.
[0142] An ideal shape of the illumination optical system according
to the present embodiment is described with reference to FIG. 7.
FIG. 7 is a cross-sectional view of a flashlight emitting apparatus
taken along the radial direction of the flashlight discharge tube
7. FIG. 7 shows the positional relation between a cover 9 serving
as an outer member of the camera body 26 and the illumination
optical system. As explained above, it is the outgoing surface 6b
of the optical prism 6 that functions as the outgoing aperture
portion of the illumination optical system, so that the cover 9 is
formed such that only the outgoing surface 6b is exposed to the
outside of the camera. Thus, the size (with respect to the vertical
direction of the apparatus) of the aperture portion formed by the
cover 9 can be made small, and the characteristic features of the
illumination optical system of the present embodiment can be
utilized best.
[0143] Moreover, the tip portions 6j of the optical prism 6 that
are formed on the light source side are configured such that they
extend to a position corresponding to the light source center, as
shown in FIG. 7. The reason for this is that if the tip portions 6j
of the optical prism 6 are positioned further to the front of the
apparatus than a position corresponding to the light source center,
then those components of the light rays emitted from the light
source that are emitted at an angle of substantially 90.degree. to
the optical axis (i.e. upward or downward in FIG. 7) cannot be
picked up, and the light rays emitted from the light source cannot
be condensed efficiently.
[0144] If, on the other hand, the tip portions 6j of the optical
prism 6 are formed such that they extend to the rear of the
apparatus behind the position corresponding to the light source
center so as to try to gather efficiently all of the light emitted
from the light source, then the optical prism 6 becomes large. And
moreover, it becomes difficult to totally reflect the light rays
emitted from the light source at the reflection surfaces 6d and
6d', and the components leaking from the optical prism 6 increase,
so that the light rays emitted from the light source cannot be
utilized efficiently.
[0145] For this reason, with regard to the condensing efficiency
and size of the illumination optical system, it is preferable that
the tip portions 6j of the optical prism 6 are formed to a position
that substantially matches the position of the light source
center.
[0146] As mentioned above, the reflection screen 8 has a
semi-circular tube portion 8a that is concentric to the light
source center, and at both ends of the semi-circular tube portion
8a, there are lateral portions 8b that are formed in one piece with
the semi-circular portion 8a, and that are bent to the rear of the
apparatus with respect to the tip portions 6j of the optical prism
6.
[0147] As shown in the ray tracing diagrams in FIGS. 9 and 10, the
light rays emitted from the light source center do not leak from
the total reflection surfaces 6d and 6d' of the optical prism 6,
but within the light rays emitted from a position that is slightly
off the center of the light source, there are light rays that leak
from the total reflection surfaces 6d and 6d'. For this reason, by
providing the reflection screen 8 with the lateral portions 8b, the
light rays leaked from the total reflection surfaces 6d and 6d' are
reflected at the lateral portions 8b, and are incident again from
the total reflection surfaces 6d and 6d' of the optical prism
1.
[0148] As shown in FIG. 7, the lateral portions 8b of the
reflection screen 8 are formed along the total reflection surfaces
6d and 6d' of the optical prism 6, so that also the light that is
reflected at the lateral portions 8b and incident again at the
total reflection surfaces 6d and 6d' can be effectively utilized as
object illumination light.
[0149] The following is an explanation of the ideal shape of the
optical prism 6. Regarding the shape of the optical prism 6 of the
present embodiment, the same shape as the ideal shape of the
optical prism 1 explained in Embodiment 1 is preferable. The
following is a discussion, applying actual numbers, of whether the
Expressions (1) and (2) explained in Embodiment 1 are also true for
the optical prism 6 of the present embodiment.
[0150] In the present embodiment, the aperture height D of the
outgoing surface 6b of the optical prism 6 is 3.0 mm, and the
maximum height A of the total reflection surfaces 6d and 6d' of the
optical prism 6 is 4.69 mm. From these numbers, it follows that the
value of D/A in Expression (1) is 0.64, which is within the range
of Expression (1).
[0151] In the present embodiment, the distance L from the tips of
the outgoing surface 6b of the optical prism 6 to the maximally
outer contour of the total reflection surfaces 6d and 6d' of the
optical prism 6 is 1.4 mm, and the distance B from the maximally
outer contour of the total reflection surfaces 6d and 6d' of the
optical prism 6 to the light source center is 3.34 mm. From these
numbers, it follows that L/B in Expression (2) is 0.42, which is
within the range of Expression (2).
[0152] Referring to FIG. 11, the following is an explanation of the
structure of the flashlight emitting apparatus with regard to the
axial direction of the flashlight discharge tube 7. FIG. 11 is a
cross-sectional view of a flashlight emitting apparatus taken along
the axial direction of the flashlight discharge tube 7, and the
same numerals are given to members corresponding to those explained
for FIGS. 7 to 10.
[0153] Reflection surfaces 6e and 6e' are formed on the lateral
surface of the optical prism 6, but different from Embodiment 1,
these reflection surfaces 6e and 6e' are formed with an evading
shape such that light rays incident the optical prism 6 will not be
incident on the reflection surfaces 6e and 6e', and the refraction
optical system made of a Fresnel lens that is arranged on the
outgoing surface side of the optical prism 6 is not affected.
[0154] Another characteristic feature of the shape of the outgoing
surface 6b of the optical prism 6 is that the end faces located at
both ends in longitudinal direction of the outgoing surface 6b are
slanted surfaces 6f and 6f'. Thus, it can be repressed that light
rays that are emitted from the light source and that are directed
within the necessary irradiation angle range escape at the two ends
of the outgoing surface 1b, and the distracting sensation at the
seam to the cover 9 serving as the outer member of the camera body
26 can be eliminated.
[0155] On the other hand, the shape of the central region of the
outgoing surface 6b differs greatly from that in Embodiment 1. That
is to say, the central region of the outgoing surface 6b is
configured as a cylindrical lens having a negative refractive
power, and is configured such that it does not adversely affect the
condensing effect with regard to the vertical direction of the
apparatus. Moreover, the peripheral regions of the outgoing surface
6b outside the central region are provided with a plurality of
small prism surfaces 6h and 6h' and Fresnel lens surfaces 6i and
6i'.
[0156] The peripheral regions of the outgoing surface 6b (that is,
the small prism surfaces 6h and 6h' as well as the Fresnel lens
surfaces 6i and 6i') are configured such that, while taking
advantage of the above-described condensing ability of the
flashlight discharge tube 7 with regard to the radial direction,
also the condensing ability of the flashlight discharge tube 7 with
regard to the axial direction is increased. Thus, it is possible to
realize an illumination optical system with an overall very high
condensing ability, due to the condensing effects in the radial
direction and the axial direction of the flashlight discharge tube
7.
[0157] In this embodiment, an example of an illumination optical
system was shown in which the light rays emitted from the
flashlight discharge tube 7 serving as the light source are
condensed to an extremely narrow range by using an optical prism 6.
However, the present invention is not limited to the form of the
optical prism 6 in the above-described Embodiment 2.
[0158] For example, the outgoing surface 6b of the optical prism 6
in the present embodiment includes a plurality of small prism
surfaces 6h and 6h' and Fresnel lens surfaces 6i and 6i' whose
vertical angle is a constant angle, but it is not necessarily
required to include both, and instead it is also possible to
include only one of the two. Moreover, in the present embodiment,
the outgoing surface 6b of the optical prism 6 includes a
cylindrical lens having negative refractive power, but it is not
necessarily required to include this cylindrical lens having
negative refractive power, and instead of a cylindrical lens, it is
also possible to use a plurality of prisms having with constant
vertical angle. Moreover, the peripheral regions of the outgoing
surface 6b are configured with Fresnel lenses, but these regions
can also be configured with lenses having positive refractive
power.
[0159] Embodiment 3
[0160] Referring to the drawings, the following is a description of
a flashlight emitting apparatus (illumination apparatus) according
to Embodiment 3 of the present invention. FIGS. 13 to 19 illustrate
a flashlight emitting apparatus according to this embodiment. The
flashlight emitting apparatus of this embodiment is of the type in
which the irradiation angle can be varied.
[0161] FIGS. 13 and 14 are cross-sectional views of the flashlight
emitting apparatus, along the radial direction of the flashlight
discharge tube. FIGS. 15 and 16 are diagrams in which ray tracing
of the light emitted from the light source center has been added to
the cross-sectional views of FIG. 13 and 14. FIG. 17 illustrates
the shape of the optical prism. FIG. 18 is a cross-sectional view
of a flashlight emitting apparatus along the axial direction
(longitudinal direction) of the flashlight discharge tube, and FIG.
19 is an exploded perspective view showing the structure of the
essential components of the flashlight emitting apparatus.
[0162] FIG. 19, which is an exploded perspective view illustrating
the internal structure of the flashlight emitting apparatus, shows
the essential components of the flashlight emitting apparatus, but
does not show holding members or lead wires.
[0163] In FIG. 19, numeral 101 denotes a first optical prism that
is arranged on the light source side of the flashlight emitting
apparatus. Numeral 102 denotes a second optical prism that is
arranged further to the front of the apparatus than the first
optical prism 101. These optical prisms 101 and 102 are made of a
glass material or optical resin material with high transmittivity
such as acrylic resin.
[0164] Numeral 103 denotes a tube-shaped flashlight discharge tube
(xenon tube) that emits flashlight when a trigger signal is input
into it. Numeral 104 denotes a reflection screen that reflects to
the emission side (to the front of the apparatus) those components
of the light rays emitted from the flashlight discharge tube 103
that have been emitted to the rear of the apparatus. The inner
surface (reflection surface) of this reflection screen 104 is made
of a metallic material having high reflectivity, such as brilliance
aluminum or the like.
[0165] The flashlight emitting apparatus of this embodiment is
provided in a camera as described in Embodiment 1 (FIG. 6). In the
following, members that are the same as those described in FIG. 6
are given the same numerals.
[0166] The following is a description of the camera operation, when
a camera provided with a flashlight emitting apparatus of the
present embodiment has been set to the "strobe auto-mode," for
example.
[0167] When the user pushes the release button 21 half down, the
brightness of the external light is measured by the light metering
device, and the result of the light measurement is sent to a
central processing unit arranged inside the camera body 26.
Depending on the brightness of the external light and the
sensitivity of the imaging medium (film or image pickup element,
such as a CCD), the central processing unit judges whether the
flashlight emitting apparatus should emit light or not.
[0168] Then, if it is judged that the flashlight emitting apparatus
should emit light, then, by giving out a light emission signal to
the flashlight emitting apparatus when the release button 21 is
pushed completely down, the central processing unit lets the
flashlight discharge tube 103 emit light via a trigger lead wire
(not shown in the drawings) that is attached to the reflection
screen 104. Here, those light rays emitted from the flashlight
discharge tube 103 that are emitted in the direction opposite from
the illumination direction (to the front of the apparatus) are
reflected by the reflection screen 104 arranged at the rear of the
apparatus and are guided in the irradiation direction. Moreover,
the light rays that are emitted in the irradiation direction are
directly incident on the first optical prism 101 arranged at the
front of the apparatus, and after being incident on the second
optical prism 102 and converted to predetermined light distribution
characteristics, they are irradiated onto the object.
[0169] The main aspects of the flashlight emitting apparatus of the
present embodiment are that the size, in the vertical direction of
the apparatus, of the outgoing aperture portion of the second
optical prism 102 that has been arranged on the object side (to the
front of the apparatus) as can be made small, as explained below,
and the light distribution characteristics can be optimized.
Referring to FIGS. 13 to 17, the following is a more detailed
description of a method for setting the optimum shape of the
flashlight emitting apparatus (optical prisms 101 and 102).
[0170] FIGS. 13 to 17 are vertical cross-sectional views of the
flashlight emitting apparatus, taken along the radial direction of
the flashlight discharge tube. In these drawings, numeral 101
denotes the first optical prism, which condenses the light rays
emitted from the light source (the flashlight discharge tube 103)
to substantially one point on the optical axis in a plane including
the radial direction of the flashlight discharge tube 103. Numeral
102 denotes the second optical prism, which has negative refractive
power and is arranged further to the light source side than the
focus point of the light rays formed by the first optical prism
101.
[0171] In the present embodiment, the relative distance in the
optical axis direction between the first optical prism 101 and the
second optical prism 102 can be changed, and thus the irradiation
angle range of the light rays (illumination light) that are
irradiated from the flashlight emitting apparatus can be changed.
The driving of the first optical prism 101 and the second optical
prism 102 is performed by an illumination driving mechanism (not
shown in the drawings), which is linked to a zoom driving mechanism
performing the zoom driving of the image-taking optical system.
With this structure, the irradiation angle range of the flashlight
emitting apparatus can be changed in accordance with the zooming of
the image-taking optical system.
[0172] Numeral 103 denotes a tube-shaped flashlight discharge tube,
which emits flashlight when a trigger signal is input into it.
Numeral 104 denotes a reflection screen, which has a semi-circular
tube portion 104a that is concentric to the flashlight discharge
tube 103, and numeral 105 denotes a cover serving as an outer
member of the camera body 26.
[0173] As shown in FIGS. 13 and 14, the second optical prism 102 is
fastened integrally to the cover 105 by gluing or the like. On the
other hand, the first optical prism 101 is fastened to the
flashlight discharge tube 103 and the reflection screen 104 by a
holding member (not shown in the drawings) in a state in which a
predetermined positional relation to those members is preserved.
Moreover, the unit made of the first optical prism 101, the
flashlight discharge tube 103 and the reflection screen 104 can be
moved in the optical axis direction by a driving mechanism, which
is not shown in the drawings.
[0174] FIGS. 13 and 15 show the positional relation of the optical
prisms 101 and 102 in the flashlight emitting apparatus of the
present embodiment when the light rays emitted from the light
source are condensed the most, that is, when the irradiation angle
range is the narrowest. On the other hand, FIGS. 14 and 16 show the
positional relation of the optical prisms 101 and 102 in the
flashlight emitting apparatus of the present embodiment when the
light rays emitted from the light source diverge uniformly, that
is, when the irradiation angle range is the broadest.
[0175] In addition to the cross section views of FIGS. 13 and 14,
FIGS. 15 and 16 also show the tracing of representative light rays
emitted from a radially central portion of the flashlight discharge
tube 103, and illustrate the distribution of the light rays emitted
from the light source center as they travel toward the object. It
should be noted that in FIGS. 13 to 16, apart from positional
relation in the optical axis direction, the structure and shape of
the optical system is the same.
[0176] With the flashlight emitting apparatus of the present
embodiment, by combining the two optical prisms 101 and 102, the
size of the overall illumination optical system can be made small,
and the irradiation angle range can be gradually changed while
keeping the light distribution characteristics uniform. Moreover,
the most important characteristic feature of the present embodiment
is that the height (in the vertical direction of the apparatus) of
that aperture portion with which light is irradiated to the outside
of the apparatus can be made small. The following is a detailed
description of the characteristics of the shape of the illumination
optical system and the behavior of the light rays that are emitted
from the flashlight discharge tube 103.
[0177] First, the behavior of the light rays in an actual
illumination optical system is described using the ray tracing
diagrams shown in FIGS. 15 and 16. FIG. 15 shows the inner and
outer diameter of a glass tube serving as the flashlight discharge
tube 103. As for the light-emitting phenomenon of the flashlight
discharge tube 103 with which the flashlight emitting apparatus is
provided, it can be assumed that, in order to improve the light
emission efficiency, light emission is mostly caused at the entire
inner diameter of the flashlight discharge tube 2, and light
emission is substantially uniform at the entire inner diameter of
the flashlight discharge tube 103.
[0178] On the other hand, at the design stage, in order to
efficiently control the light that is emitted from the flashlight
discharge tube 103 serving as the light source, it is preferable to
design the shape of the illumination optical system under the
assumption that there is an ideal point light source at the center
of the light source, rather than simultaneously taking into account
all light rays over the entire inner diameter of the flashlight
discharge tube 103. Then, efficient design is possible if, after
the shape of the illumination optical system has been designed, a
correction is performed in consideration of the fact that the light
source has a finite size. Also this embodiment follows this
approach, and the center of the light source is taken as the
reference value when determining the shape of the illumination
optical system, and the shape of all the portions of the optical
prisms 101 and 102 is set as described below.
[0179] First, the shape of the first optical prism 101, which can
also be said to be the most significant characteristic feature of
the present embodiment, is explained in detail with reference to
FIG. 17. FIG. 17 shows the state when the second optical prism 102
has been removed from the state shown in FIGS. 15 and 16, and shows
a ray tracing diagram of the light rays emitted from the light
source center.
[0180] As shown in FIG. 17, the first optical prism 101 condenses
the light rays emitted basically from the light source center on
one point O (focus point) on the optical axis. The shape of the
various portions of the first optical prism 101 is described in
detail in the following.
[0181] First, those components of the light rays emitted from the
light source center for which the angle formed with the optical
axis is small are incident on the ingoing surface 101a that is
provided on the light source side of the first optical prism 101.
This ingoing surface 101a is made of a cylindrical lens with a
convex surface. Then, the light rays that have passed through the
ingoing surface 101a pass through the outgoing surface 101b, and
are condensed onto the focus point O.
[0182] On the other hand, those components of the light rays
emitted from the light source center for which the angle formed
with the optical axis is large are incident on the ingoing surfaces
101c and 101c' that are formed on the light source side of the
first optical prism 101, and after they have been refracted by
these ingoing surfaces 101c and 101c', they are guided to the total
reflection surfaces (reflective portions) 101d and 101d'. Then, the
light rays reflected at the total reflection surfaces 101d and
101d' pass through the outgoing surface 101b and are condensed onto
the focus point O on the optical axis.
[0183] The light rays emitted from the light source center that
travel toward the rear of the apparatus are reflected by the
reflection screen 104. The reflection screen 104 has a
semi-circular tube portion 104a that is concentric to the
tube-shaped flashlight discharge tube 103, so that the light rays
that are reflected by the semi-circular tube portion 104a of the
reflection screen 104 are guided back to the vicinity of the light
source center. After that, they are condensed onto the focus point
O on the optical axis, taking the same optical path as the light
rays traveling toward the emission direction from the light source
center, as described above. As a result, basically all light rays
emitted from the light source center are condensed on the focus
point O on the optical axis.
[0184] Here, the surface shape of the outgoing surface 101b of the
first optical prism 101 is determined such that all the light rays
incident on this surface are incident on it at a substantially
right angle (that is, in normal direction). If the surface shape of
the outgoing surface 101b were not determined in this manner, then
there would be components with light loss due to surface
reflections at the outgoing surface 101b, when the light rays are
emitted from the first optical prism 101.
[0185] Furthermore, as shown in FIG. 17, the light rays emitted
from the light source center reach the outgoing surface 101b of the
optical prism 101 without crossing one another, and moreover,
arranged next to one another in order on the outgoing surface 101b
with respect to the angles at which they are emitted from the light
source center.
[0186] The ingoing surfaces 101c and 101c' of the optical prism 101
are made of surfaces forming a relatively large angle with the
optical axis, because, if the inclination angle of the ingoing
surfaces 101c and 101c' with respect to the optical axis were
small, then some components of the light rays emitted from the
light source center would undergo total reflection at the ingoing
surfaces 101c and 101c', and the light rays emitted from the light
source would be directed in a direction that is different from the
intended direction of the ray tracing shown in FIG. 17. Thus, by
providing the ingoing surfaces 101c and 101c' with a predetermined
inclination, the present embodiment prevents the occurrence of
components that are totally reflected by the ingoing surfaces 101c
and 101c'.
[0187] Thus, by devising the shapes of the various parts of the
optical prism 101 as described above, the light rays emitted from
the light source can be condensed on the focus point O on the
optical axis, allowing a structure that is suitable for configuring
an illumination optical system with which the irradiation angle
range can be varied, as described below.
[0188] The following is a description of the positional relation
between the optical prisms 101 and 102 of the flashlight emitting
apparatus of the present embodiment, when changing the irradiation
angle.
[0189] In the state shown in FIG. 13 and 15, the light rays emitted
from the flashlight emitting apparatus are condensed the most. In
this state, the outgoing surface 101b of the first optical prism
101 and the ingoing surface 102a of the second optical prism 102a
are the closest. In the present embodiment, the outgoing surface
101b of the optical prism 101 and the ingoing surface 102a of the
optical prism 102a are formed with such shapes that they can be
fitted to one another without a gap, so that in this state the
optical prism 101 and the optical prism 102 are substantially in
surface contact with one another.
[0190] On the other hand, the outgoing surface (negative lens
portion) 102b of the second optical prism 102 is configured by an
extremely concave cylindrical lens, so that light rays passing
through this surface are converted such that they travel in a
direction substantially parallel to the optical axis. Moreover, by
arranging the second optical prism 102 such that the outgoing
surface 102 is positioned more on the light source side than the
focus point O, as shown in FIG. 17, the light rays from the light
source can be emitted with high condensing efficiency from the
outgoing surface 102b.
[0191] The state shown in FIG. 15 is the most extreme state, and by
converting the light rays emitted from the light source center with
the first optical prism 101 and the second optical prism 102 into
light rays that are parallel to the optical axis, it is possible to
attain a state in which the irradiation angle range is narrowest
and the condensing degree is the highest.
[0192] On the other hand, FIGS. 14 and 16 are diagrams showing the
state when the first optical prism 101 and the second optical prism
102 are spaced apart by a certain distance L. As shown in these
drawings, by increasing the distance between the first optical
prism 101 and the second optical prism 102, it is possible to
change from the most condensed state shown in FIG. 15 to a state in
which the light rays emitted from the light source center are
broadened by an irradiation angle range .theta., as shown in FIG.
16.
[0193] FIGS. 15 and 16 respectively show the states with the
narrowest and the broadest irradiation angle range, but the
irradiation angle ranges of the flashlight emitting apparatus of
this embodiment are not limited to these two states. That is to
say, by stopping the first optical prism 101 at a suitable
position, and changing the distance between the first optical prism
101 and the second optical prism 102, it is possible to set the
irradiation angle range to any range between the state shown in
FIG. 15 and the state shown in FIG. 16. Moreover, it is possible to
change the irradiation angle range gradually during the movement
stroke of the first optical prism 101, and to convert the light
emitted from the light source for any irradiation angle range such
that it has a uniform light distribution.
[0194] Thus, by arranging the second optical prism 102 having a
negative refractive power at a position that is closer to the light
source side than the focus point O that is formed by the light rays
emitted from the first optical prism 101, and by changing the
positional relation of the two optical prisms on the optical axis,
it is possible to change the irradiation angle range.
[0195] As can be seen from FIGS. 15 and 16, the change of this
irradiation angle range is determined by the position with respect
to the focus point O of the outgoing surface 102b (concave lens
surface) of the second optical prism 102. That is to say, as shown
in FIG. 15, a high condensing ability can be obtained when the
light rays emitted from the light source pass through all of the
regions of the outgoing surface 102b of the second optical prism
102.
[0196] Furthermore, as shown in FIG. 16, when the light rays pass
only through the region of the outgoing surface 102b with small
curvature near the optical axis, then the irradiation angle range
is broadened by weakening the condensing power, and uniform light
distribution characteristics can be attained over this broad
range.
[0197] On the other hand, as shown in FIGS. 13 to 16, the region of
the outgoing surface 102b of the second optical prism 102 (region
through which the light rays emitted from the light source center
in the outgoing surface 102b) becomes narrower than the region of
the outgoing surface 101b of the first optical prism 101 (region
through which the light rays emitted from the light source center
in the outgoing surface 101b), and from immediately before entering
the first optical prism 101 until immediately after leaving the
second optical prism 102, the irradiation angle range becomes
extremely narrow. For this reason, the light rays can be emitted
with high condensing efficiency from a narrow outgoing aperture
portion.
[0198] Moreover, the light rays that have passed through the
ingoing surface (positive lens portion) 101a and the light rays
that have passed through the ingoing surfaces 101c and 101c' of the
first optical prism 101 are all emitted from the outgoing surface
101b, and this outgoing surface 101b is configured as a
continuously curved surface. Thus, machining of the outgoing
surface 101b becomes easy, and discrepancies due to machining
precision or positional shifts when assembling the illumination
optical system do not occur. That is to say, even when the position
of the light rays that reach the outgoing surface 101b is slightly
shifted, this hardly affects the optical characteristics, and
consistent optical characteristics without irregularities in the
light distribution can be attained, because there are no
discontinuities in the outgoing surface 101b and the changes in the
surface shape are small.
[0199] The above is also the same when assuming that the size of
the light source has a certain constant size, so that considerable
changes in the optical characteristics also tend not to occur and
continuous changes in the optical characteristics are attained with
respect to changes in the size of the light source. Thus, this
structure is advantageous for providing illumination optical
systems with a uniform light distribution.
[0200] Moreover, the outgoing surface 102b of the second optical
prism 102 is not made of a complicated surface, but of a single
concave surface, so that, in addition to the above-described
effects of the outgoing surface 101b, there is the advantage that
it can also be used directly as an external component of the
flashlight emitting apparatus.
[0201] One of the most significant characteristic features of this
embodiment is that in the illumination optical system using the
optical prisms 101 and 102, it is possible to reduce the size of
only the outgoing surface 102b, while taking advantage of the
characteristic features of miniaturization and high condensing
efficiency. That is to say, the total length and height required
for the illumination optical system is made much smaller than in
the prior art, and if the light source is tiny enough, then there
are clearly no light rays for which light loss occurs. And
moreover, the outgoing aperture portion (outgoing surface 102b) of
the flashlight emitting apparatus that is apparent (i.e. that can
be seen from outside the camera) can be made smaller, while making
the overall illumination optical system smaller.
[0202] Referring to FIGS. 13 and 14, the following is a description
of the ideal shape of the illumination optical system of the
present embodiment. FIGS. 13 and 14 are cross-sectional views of a
flashlight emitting apparatus taken along the radial direction of
the flashlight discharge tube 103, and show the positional relation
between a cover 105 serving as an outer member of the camera body
26 and the illumination optical system.
[0203] As illustrated in FIGS. 15 and 16, it is the outgoing
surface 102b of the second optical prism 102 that functions as the
outgoing surface of the illumination optical system, so that the
cover 105 is formed such that also at the outgoing aperture portion
of the illumination optical system of the camera, only the outgoing
surface 102b is exposed to the outside of the camera. Thus, the
size (with respect to the vertical direction of the camera) of the
outgoing aperture portion of the illumination optical system can be
made such that it looks the smallest, and the characteristic
features of the present embodiment can be utilized best.
[0204] Moreover, the tip portions 101e of the first optical prism
101 that are formed on the light source side are configured such
that they extend to a position corresponding to the light source
center, as shown in FIGS. 13 and 14. The reason for this is that if
the tip portions 101e of the optical prism 101 are positioned
further to the front of the apparatus than a position corresponding
to the light source center, then those components of the light rays
emitted from the light source that are emitted at an angle of
substantially 90.degree. to the optical axis (i.e. upward or
downward in the drawings) cannot be picked up, and the light rays
emitted from the light source cannot be condensed efficiently.
[0205] If, on the other hand, the tip portions 101e of the optical
prism 101 are formed such that they extend to the rear of the
apparatus behind the position corresponding to the light source
center so as to try to gather all of the light emitted from the
light source with high efficiency, then the overall optical prism
(first optical prism 101) becomes large. And moreover, it becomes
difficult to totally reflect the light rays emitted from the light
source with the reflection surfaces 101d and 101d', and the
components leaking from the optical prism 101 increase, so that the
light rays emitted from the light source cannot be utilized
efficiently.
[0206] For this reason, with regard to the condensing efficiency
and size of the illumination optical system, it is preferable that
the tip portions 101e of the optical prism 101 are formed to a
position that substantially matches the position of the light
source center.
[0207] As mentioned above, the reflection screen 104 has a
semi-circular tube portion 104a that is concentric to the light
source center, and at both vertical ends of the semi-circular tube
portion 104a, there are lateral portions 104b that are formed in
one piece with the semi-circular portion 104a, and that are bent
behind the tip portions 101e of the optical prism 101. As shown in
the ray tracing diagrams in FIGS. 15 and 16, the light rays emitted
from the light source center do not leak from the total reflection
surfaces 101d and 101d' of the optical prism 101, but within the
light rays emitted from a position that is slightly off the center
of the light source, there are light rays that leak from the total
reflection surfaces 101d and 101d'. For this reason, by providing
the lateral portions 104b, the light rays leaked from the total
reflection surfaces 101d and 101d' are incident again from the
total reflection surfaces 101d and 101d' of the optical prism
101.
[0208] As shown in FIGS. 13 and 14, the lateral portions 104b of
the reflection screen 104 are formed along the total reflection
surfaces 101d and 101d' of the optical prism 101, so that also the
light that is reflected at the lateral portions 104b and incident
again at the total reflection surfaces 101d and 101d' can be
effectively utilized as object illumination light.
[0209] The following is an explanation of the ideal shape of the
optical prisms 101 and 102. First, the ideal shape of the
dimensions in vertical direction of the illumination optical system
is explained.
[0210] In FIG. 13, it is preferable that the aperture height D of
the outgoing surface 102b of the second optical prism 102 is within
the range of the Expression (3) below. That is, the ratio between
the aperture height D of the outgoing surface 102b of the second
optical prism 102 and the maximum height A constituted by the total
reflection surfaces 101d and 101d' of the first optical prism is
given by:
0.4.ltoreq.D/A.ltoreq.0.8 (3)
[0211] In order to adapt to new camera designs, it would be ideal
to make the aperture height D as narrow as possible, but depending
on the size of the flashlight discharge tube 103 serving as the
light source, the light loss becomes larger as the length of the
aperture height D is shortened, and it may not be possible to
configure an effective condensing optical system.
[0212] That is to say, if the aperture height D of the outgoing
surface 102b in the vertical direction of the apparatus is reduced,
and the size of the light source (diameter of the flashlight
discharge tube 103) is increased, the light that travels directly
to the outgoing surface 102b of the second optical prism 102 is
reduced, and the components that repeatedly undergo-total
reflection inside the optical prisms 101 and 102 are increased. As
a result, most of the components that would have been emitted from
the outgoing surface 102b are emitted from other portions of the
optical prisms 101 and 102, and those components of the light rays
emitted from the light source that can be used effectively for the
illumination of the object are decreased. Consequently, with the
above structure, even though the aperture height D in the vertical
direction of the apparatus is reduced, it is still not necessarily
an ideal illumination optical system with regard to the effective
utilization of light rays emitted from the light source.
[0213] With regard to this, the lower limit of Expression (3) is
the aperture height D that functions effectively as the
illumination optical system, if the size (diameter) of the
flashlight discharge tube 103 serving as the light source is
relatively small. And the upper limit of Expression (3) becomes the
aperture height D that functions effectively for the illumination
optical system, if the diameter of the flashlight discharge tube
103 is large.
[0214] Thus, if the diameter of the flashlight discharge tube 103
is small, the lower limit of Expression (3) is the size of the
aperture height D that functions effectively for the illumination
optical system, and it follows from the expression that the
aperture height D can be made smaller if the flashlight discharge
tube 103 is made smaller. However, due to such reasons as the
durability and the manufacturing process of the actual flashlight
discharge tube 103, there are no flashlight discharge tubes 103
below a certain diameter.
[0215] Considering the diameter of flashlight discharge tubes 103
that can be manufactured in practice, then a lower limit for D/A of
0.4 seems appropriate.
[0216] On the other hand, if the upper limit 0.8 for D/A in
Expression (3) is exceeded, then the aperture height D becomes
large, which is not desirable with regard to the object of the
present invention, namely to reduce the size of the outgoing
aperture portion in the vertical direction of the apparatus.
[0217] The following is a discussion of actual numbers for
Expression (3) in a flashlight emitting apparatus according to the
present embodiment. In the present embodiment, the diameter (inner
diameter) of the flashlight discharge tube 2 is .phi.1.3 mm, the
maximum height A of the total reflection surfaces 101d and 101d' of
the first optical prism 101 is 6.8 mm, and the aperture height D of
the outgoing surface 102b of the second optical prism 102 is 4.5
mm. From these numbers, it follows that the value of the aperture
ratio (D/A) in Expression (3) is 0.66, which is within the range of
Expression (3).
[0218] The following is an explanation of the positional relation
of the optical prisms 101 and 102 in the optical axis direction.
When L is the spacing between the first optical prism 101 and the
second optical prism 102 (see FIG. 14), and B is the distance
between the outgoing surface 101b of the first optical prism 101
and the focus point O (see FIG. 17), then it is preferable that the
ratio of the distance L and the distance B satisfies the following
Expression (4):
0.ltoreq.L/B.ltoreq.1.0 (4)
[0219] With regard to making the illumination optical system small,
the distance L is ideally as short as possible. However, a certain
length (L) is necessary in order to make the size of the outgoing
surface 102b of the second optical prism 102 with respect to the
vertical direction of the apparatus small. Moreover, considering
the thickness of the cover 105 of the camera body 26, a certain
length will be necessary in order to let the outgoing surface 102b
of the second optical prism 101 look tiny in the vertical direction
of the apparatus.
[0220] In the present embodiment, considering these two aspects,
the relation of the distance L and the distance B is set such that
the Expression (4) is satisfied.
[0221] The lower limit 0 in Expression (4) means the state when the
first optical prism 101 and the second optical prism 102 are in
contact, and this lower limit cannot be undercut. On the other
hand, the upper limit is set to 1.0, because when a larger value is
taken, then the illumination optical system becomes large in the
optical axis direction, and the goal of making the illumination
optical system smaller, which is one of the results of the present
embodiment, is missed. Moreover, when the distance between the
optical prisms 101 and 102 is L/B >1.0, then the light rays
directed toward the central region of the outgoing surface 102b
become very few, and preferable light distribution characteristics
is not likely to be obtained.
[0222] The following is a discussion of actual numbers for
Expression (4) in a flashlight emitting apparatus according to the
present embodiment. In the present embodiment, the distance L
(maximum distance between the optical prisms 101 and 102) is 3 mm
and the distance B is 5 mm. From these numbers, it follows that L/B
is 0.6, which is within the range of Expression (4).
[0223] In the present embodiment, the outgoing surface 101b of the
first optical prism 101 is configured as a curved surface on which
light rays are incident substantially perpendicularly (that is, in
normal direction), in order to reduce the light loss. However, the
shape of the outgoing surface 101b is not necessarily limited to
this curved shape.
[0224] For example, it is also possible to make the curvature of
the outgoing surface 101b softer, or in the extreme case, planar.
In that case, the focus point O becomes closer to the outgoing
surface 101b of the first optical prism 101, and it becomes
possible to change the irradiation angle considerably with a small
movement distance.
[0225] However, when the focus point O approaches the light source
side, there are more light components for which the outgoing angle
from the outgoing surface 101b and the optical axis becomes sharp,
and it becomes difficult to condense the light on one point on the
optical axis, the design of a concave surface (outgoing surface
101b) with which the condensing can be controlled with the second
optical prism 102 becomes difficult, and the light loss due to
total reflections inside the optical prism becomes large. And
moreover, damage may occur because the lens thickness of the second
optical prism 102 becomes more difficult to take away.
[0226] However, for an illumination optical system with a variable
irradiation angle, an embodiment is advantageous with which
miniaturization is possible.
[0227] In the present embodiment, the outgoing surface 101b of the
first optical prism 101 and the ingoing surface 102a of the second
optical prism 102 were configured as concave and convex cylindrical
lenses whose surface shapes fit into one another without a gap.
However, the shape of the two is not limited to this combination,
and they do not necessarily have to fit against one another.
[0228] It is also possible to use different surface structures and
to make the outgoing surface 101b of the first optical prism 101
planar and the ingoing surface 102a of the second optical prism 102
concave, for example. In any case, at least one of the ingoing
surface 102a and the outgoing surface 102b of the second optical
prism 102 should be concave, and overall, the second optical prism
102 should have a negative refractive power.
[0229] Thus, even if the shape of the outgoing surface 101b of the
first optical prism 101 is changed, the irradiation angle range can
be changed by moving the first optical prism 101 in the optical
axis direction. Also in this case, it is preferable that the first
optical prism 101 is moved within a range in which the above-noted
Expression (4) is satisfied. Thus, it is possible to realize an
illumination apparatus with a small outgoing aperture portion,
without making the shape of the optical prisms constituting the
illumination optical system unnecessarily large. Moreover, the
above-described structure does not compromise the changing of the
irradiation angle range, so that the irradiation angle range can be
changed with relatively high efficiency.
[0230] Referring to the cross-sectional view shown in FIG. 18, the
following is an explanation of the shape of the flashlight emitting
apparatus with regard to the axial direction of the flashlight
discharge tube 103. It should be noted that in this drawing, the
same numerals are given to members corresponding to those explained
for FIGS. 13 to 17.
[0231] A characteristic feature of the shape of the second optical
prism 2 is that its lateral sides in longitudinal direction are
provided with total reflection surfaces 102e and 102e'. Thus, those
light rays emitted from the light source that deviate from the
necessary irradiation angle range can be guided into the necessary
irradiation angle range, and the light from the light source is
utilized effectively. Another characteristic feature of the shape
of the outgoing surface side of the second optical prism 102 is
that in order to prevent that light rays that are reflected by the
total reflection surfaces 102e and 102e' and travel in a
predetermined direction are adversely effected by the following
refraction, the corresponding surfaces 102f and 102f' on the
outgoing surface side are planar. Moreover, by making the
corresponding surfaces 102 and 102f' planar, the distracting
sensation at the seam to the cover 105 of the camera body 26 can be
eliminated can be eliminated.
[0232] The following is a description of the shape on the outgoing
surface side of the other portions of the second optical prism 102.
The shape at the region around the central portion (central region
102j) is formed merely as a cylindrical lens having negative
refractive power, and the condensing effect in the vertical
direction of the apparatus is not adversely affected. Moreover, to
the left and right of the central region 102j of the outgoing
surface 102b, a plurality of small prism surfaces 102h and 102h'
are formed. And in the regions outside the small prism surfaces
102h and 102h', Fresnel lens surfaces 102 and 102i' are formed.
[0233] The shape of the above-described outgoing surface 102b
increases the condensing ability in the axis direction of the
flashlight discharge tube 103 while taking advantage of the
condensing ability in the radial direction of the straight
tube-shaped flashlight discharge tube 103 shown in FIGS. 13 to 17,
and an illumination whose overall condensing ability is very high
is realized with these two types of condensing effects.
[0234] In this embodiment, an example of an illumination optical
system was shown in which the light rays emitted from the light
source center are condensed/diverged and the irradiation angle is
changed by the interaction of the first optical prism 101 and the
second optical prism 102.
[0235] However, the illumination optical system of the present
invention is not limited to the shape of the illumination optical
system of the present embodiment. For example, in the present
embodiment, a concave cylindrical lens is used for the outgoing
surface 101b of the first optical prism 101, but it is also
possible to configure this outgoing surface 101b with a Fresnel
lens having negative refractive power. Moreover, also the other
faces of the optical prisms can be substituted by Fresnel
lenses.
[0236] The present embodiment has been explained based on the
premise that the reflective surfaces 101d and 101d' of the first
optical prism 101 are configured as total reflection surfaces, but
they may also be devised as metal vapor deposition surfaces. In
this case, the limit for the angle of the rays incident on the
reflection surface becomes smaller, so that it is possible to
condense the light rays from the light source more efficiently and
with a smaller structure.
[0237] Moreover, the reflection screen 104 is formed as a
semi-circular tube-shaped portion 104a that is concentric to the
center of the flashlight discharge tube 103, but there is no
limitation to this shape (semi-circular tube-shaped surface), and
it is also possible to use a second-order surface, such as an
elliptical surface. If the reflection screen has an elliptical
surface, then the reflection screen can be made smaller in the
vertical direction of the apparatus.
[0238] Embodiment 4
[0239] Referring to FIGS. 20 to 26, the following is a description
of a flashlight emitting apparatus (illumination apparatus)
according to Embodiment 4 of the present invention. The flashlight
emitting apparatus of this embodiment is of the type in which the
irradiation angle can be varied.
[0240] FIGS. 20 and 21 are cross-sectional views of the flashlight
emitting apparatus, along the radial direction of the flashlight
discharge tube. FIG. 22 illustrates the shape of the condensing
optical system. FIGS. 23 and 24 are diagrams in which ray tracing
of the light emitted from the light source center has been added to
the cross-sectional views of FIG. 20 and 21. FIG. 25 is a
cross-sectional view of a flashlight emitting apparatus along the
axial direction (longitudinal direction) of the flashlight
discharge tube. FIG. 26 is an exploded perspective view showing the
structure of the essential components of the flashlight emitting
apparatus.
[0241] FIG. 26, which is an exploded perspective view illustrating
the internal structure of the flashlight emitting apparatus, shows
the essential portions of the illumination optical system, but does
not show holding members or lead wires.
[0242] In FIG. 26, numeral 131 denotes a cylindrical lens having
positive refractive power that is arranged on the light source side
of the flashlight emitting apparatus. The two faces 131a and 131b
of this cylindrical lens 131 are convex surfaces. Numeral 132
denotes an optical prism that is arranged on the outgoing side of
the flashlight emitting apparatus. The cylindrical lens 131 and the
optical prism 132 are made of a glass material or optical resin
material with high transmittivity such as acrylic resin.
[0243] Numeral 133 denotes a straight tube-shaped flashlight
discharge tube (xenon tube) that emits flashlight when a trigger
signal is input into it. Numeral 134 denotes a reflection screen
that reflects to the emission side (to the front of the apparatus)
those components of the light rays emitted from the flashlight
discharge tube 133 that have been emitted to the rear or to the
side of the apparatus. The inner side (reflection surface) of this
reflection screen 134 is made of a metallic material having high
reflectivity, such as brilliance aluminum or the like.
[0244] Different to Embodiment 3, in the flashlight emitting
apparatus of this embodiment, the condensing optical system that
condenses the light rays emitted from the light source
substantially on one point includes an additional optical system.
That is to say, in Embodiment 3, the light rays emitted from the
light source are condensed substantially on one point (the focus
point) using a single component, namely the first optical prism,
arranged on the light source side, whereas in this embodiment, the
light rays are condensed on substantially one point (the focus
point) using two components, namely the cylindrical lens 131 and
the reflection screen 134.
[0245] The flashlight emitting apparatus of this embodiment is
provided in a camera as described in Embodiment 1 (FIG. 6). In the
following, members that are the same as those described in FIG. 6
are given the same numerals.
[0246] Referring to FIGS. 20 to 24, the following is a more
detailed description of a method for setting the most suitable
shape of the illumination optical apparatus.
[0247] FIGS. 20 to 24 are vertical cross-sectional views of the
flashlight emitting apparatus, taken along the radial direction of
the flashlight discharge tube. In these drawings, numeral 131
denotes the cylindrical lens (positive lens portion), which has
positive refractive power, for condensing the light rays emitted
from the light source center on substantially one point on the
optical axis with regard to this cross section. Numeral 132 denotes
the optical prism, which has negative refractive power and which is
arranged further to the outgoing surface side than the cylindrical
lens 131.
[0248] Numeral 133 denotes a tube-shaped flashlight discharge tube
that emits flashlight when a trigger signal is input into it.
Numeral 134 denotes a reflection screen having a semi-circular tube
portion 134a that is concentric to the flashlight discharge tube
133, and elliptical portions (reflection portions) 134b and 134b'
that condense light rays emitted from the light source center on
substantially one point. Here, the condensing optical system is
made of the cylindrical lens 131 and the reflection screen 134.
Numeral 135 denotes a cover serving as an outer member of the
camera body 26.
[0249] As shown in the drawings, the optical prism 132 is fastened
integrally to the cover 135 by gluing or the like. On the other
hand, the cylindrical prism 131 is fastened to the flashlight
discharge tube 133 and the reflection screen 134 by a holding
member (not shown in the drawings) in a state in which a
predetermined positional relation to those members is preserved.
Moreover, the unit made of the cylindrical prism 131, the
reflection screen 134 and the flashlight discharge tube 133 can be
moved in the optical axis direction by a driving mechanism, which
is not shown in the drawings.
[0250] In the present embodiment, by moving this unit in the
optical axis direction and changing the distance between the unit
and the optical prism 132, it is possible to change the irradiation
angle of the light rays (illumination light) irradiated from the
flashlight emitting apparatus.
[0251] FIGS. 20 and 23 show the optical arrangement in the
flashlight emitting apparatus of this embodiment when the light
rays emitted from the light source are condensed the most, that is,
when the irradiation angle range is the narrowest. On the other
hand, FIGS. 21 and 24 show the optical arrangement in the
flashlight emitting apparatus of this embodiment when the light
rays emitted from the light source diverge uniformly, that is, when
the irradiation angle range is the broadest.
[0252] In addition to the cross sections of FIGS. 20 and 21, FIGS.
23 and 24 also show the tracing of representative light rays
emitted from a radially central portion of the flashlight discharge
tube 133, and illustrate the distribution of the light rays emitted
from the light source center as they travel toward the object. It
should be noted that in FIGS. 20 to 24, apart from positional
relation in the optical axis direction, the structure and shape of
the illumination optical system is the same.
[0253] The flashlight emitting apparatus of the present embodiment
is an illumination optical system in which, by combining the
condensing optical system made of the reflection screen 134 and the
cylindrical lens 131 with the optical prism 132 having negative
refractive power, the irradiation angle range can be gradually
changed while keeping the light distribution characteristics
uniform. Moreover, the most important characteristic feature of the
present embodiment is that the size of the aperture portion, in the
vertical direction of the apparatus, can be minimized, as in
Embodiment 3. The following is a detailed description of the
characteristics of the shape of the illumination optical system and
the behavior of the light rays that are emitted from the flashlight
discharge tube 133.
[0254] The behavior of the light rays in an actual illumination
optical system is described in detail using the ray tracing diagram
shown in FIGS. 23 and 24. First, the condensing optical system
condensing the light rays emitted from the light source on
substantially one point (focus point), which can also be said to be
the most significant characteristic feature of the present
embodiment, is described in detail with reference to FIG. 22. FIG.
22 shows the state when the optical prism 132 has been removed from
the illumination optical system shown in FIGS. 23 and 24, and shows
a ray tracing diagram of the light rays emitted from the light
source center.
[0255] As shown in FIG. 22, the cylindrical lens 131 condenses the
light rays emitted basically from the light source center
substantially on one point (focus point) O on the optical axis. The
shape of the various parts of the condensing optical system of the
present embodiment is described in detail in the following.
[0256] First, those components of the light rays emitted from the
light source center for which the angle formed with the optical
axis is small are incident on the cylindrical lens 131, whose two
faces (131a and 131b) are convex, that is provided on the light
source side. Then, the light rays that have passed through the
cylindrical lens 131 are condensed onto the focus point O.
Moreover, after the components that form a large angle with the
optical axis have been reflected by the reflection surfaces 134b
and 134b' of the reflection screen 134, they are also condensed on
the focus point O. That is to say, the reflection surfaces 134b and
134b' are formed with elliptical surfaces, taking the light source
center and the focus point O as the foci.
[0257] On the other hand, those components of the light rays
emitted from the light source center that are emitted toward the
rear of the apparatus are reflected by the reflection screen 134.
The reflection screen 134 has a semi-circular tube portion 134a
that is concentric to the tube-shaped flashlight discharge tube
133, so that the light rays that are reflected by the semi-circular
tube portion 134a of the reflection screen 134 are guided back to
the vicinity of the center of the flashlight discharge tube 133.
After that, they are condensed onto the focus point O, taking the
same optical path as the light rays traveling toward the emission
direction from the light source center, as described above. As a
result, basically all light rays emitted from the light source
center are condensed on the focus point O on the optical axis.
Moreover, FIG. 22 shows that the light rays emitted from the light
source center reach the focus point O without crossing one
another.
[0258] The size of the cylindrical lens 131 is set such that the
light rays reflected at the reflection screen 134 do not enter the
cylindrical lens 131. That is to say, after the light rays emitted
from the light source center have been reflected by the reflection
surfaces 134b and 134b', they travel toward the focus point O, but
the size of the cylindrical lens 131 is determined such that it
does not interfere with the light rays.
[0259] Thus, by devising the shapes of the various surfaces of the
condensing optical system in this manner, it is possible to
configure a condensing optical system that is suitable for
configuring an illumination optical system with which the
irradiation angle range can be varied, as described below.
[0260] Referring to FIGS. 23 and 24, the following is a description
of the structure of the flashlight emitting apparatus of the
present embodiment, with which the irradiation angle can be
changed.
[0261] FIG. 23 shows the state in which the light rays emitted from
the flashlight emitting apparatus are condensed the most. In this
state, the cylindrical lens 131 and the optical prism 132 are
closest to each other.
[0262] On the other hand, the outgoing surface (negative lens
portion) 132b of the optical prism 132 is configured by an
extremely concave cylindrical lens, so that light rays refracted by
this surface will travel in a direction substantially parallel to
the optical axis. By arranging the optical prism 132 such that the
outgoing surface 132b is positioned more on the light source side
than the focus point O shown in FIG. 22, the light rays from the
light source can be emitted with high condensing efficiency from
the outgoing surface 132b.
[0263] The state shown in FIG. 23 is the most extreme state, and by
converting all of the light rays emitted from the light source
center into light rays that are parallel to the optical axis, it is
possible to attain the state in which the irradiation angle range
is narrowest and the condensing degree is the highest.
[0264] On the other hand, FIG. 24 is a diagram showing the state
when the cylindrical lens 131 and the optical prism 132 are spaced
apart by a certain distance. As shown in FIG. 24, by increasing the
distance between the cylindrical lens 131 and the optical prism
132, it is possible to change from the most condensed state shown
in FIG. 25 to a state in which the light rays emitted from the
light source center are broadened by an irradiation angle range
.theta., as shown in FIG. 24.
[0265] FIGS. 23 and 24 respectively show the states with the
narrowest and the broadest irradiation angle range, but the
irradiation angle range of the flashlight emitting apparatus of
this embodiment are not limited to these two states. That is to
say, by stopping the condensing optical system at a suitable
position, and changing the distance between the cylindrical lens
131 and the optical prism 132, it is possible to set the
irradiation angle range to any range between the state shown in
FIG. 23 and the state shown in FIG. 24. Moreover, during the
movement stroke of the condensing optical system (including the
cylindrical lens 131), there is no position at which the light
distribution characteristics (irradiation angle range) are
discontinuous, and it is possible to convert the light emitted from
the light source such that it has a uniform light distribution at
any position of the condensing optical system.
[0266] Thus, by arranging the optical prism 132 having a negative
refractive power at a position that is closer to the light source
side than the focus point O that is formed by the light rays
emitted from the cylindrical lens 131, and by changing the
positional relation of the cylindrical lens 131 and the optical
prism 132 on the optical axis, it is possible to change the
irradiation angle range.
[0267] As can be seen from FIGS. 23 and 24, the change of this
irradiation angle range is determined by the position of the
outgoing surface 132b (concave lens surface) of the optical prism
132 with respect to the focus point O. That is to say, as shown in
FIG. 23, a high condensing ability can be obtained when the light
rays emitted from the light source pass through all of the regions
of the outgoing surface 132 of the optical prism 132.
[0268] Furthermore, as shown in FIG. 24, when the light rays pass
only through a region of the outgoing surface 132b with small
curvature near the optical axis, then the irradiation angle range
is broadened by weakening the condensing effect, and uniform light
distribution characteristics can be attained over this broad
range.
[0269] On the other hand, as shown in FIGS. 20 to 24, the aperture
portion serving as the emission region of the optical prism 132
becomes narrower than the aperture portion serving as the emission
region of the reflection screen 134, and from immediately before
entering the condensing optical system until immediately after
leaving the optical prism 132, the irradiation angle range becomes
extremely narrow. For this reason, the light rays can be emitted
with high condensing efficiency from a narrow outgoing aperture
portion of the illumination optical system.
[0270] Moreover, as in Embodiment 3, the outgoing surface 132 of
the optical prism 132 is configured not as a complicated surface
but as a continuously curved surface. Thus, machining of the
outgoing surface 132b becomes easy, and discrepancies due to
machining precision or positional shifts when assembling the
illumination optical system do not occur. That is to say, it seems
that even when the position of the light rays that reach the
outgoing surface 132b is slightly shifted, this has no significant
influence on the optical characteristics and consistent optical
characteristics without light distribution irregularities can be
attained, because there are no discontinuities in the outgoing
surface 132b, and there are no changes in the surface shape.
[0271] The above is also the same when assuming that the size of
the light source has a certain constant size, so that considerable
changes in the optical characteristics also tend not to occur and
continuous changes in the optical characteristics are attained with
respect to changes in the size of the light source. Thus, this
structure is advantageous for providing illumination optical
systems with a uniform light distribution.
[0272] Moreover, the outgoing surface 132b of the optical prism 132
is not made of a complicated surface, but of a single concave
surface, so that, in addition to the above-described effects, there
is the advantage that it can also be used directly as an external
component of the flashlight emitting apparatus.
[0273] Referring to FIGS. 20 and 21, the following is a description
of the ideal shape of the illumination optical system of the
present embodiment. FIGS. 20 and 21 are cross-sectional views of a
flashlight emitting apparatus taken along the radial direction of
the flashlight discharge tube 133 and show the positional relation
between a cover 135 of the camera body 26 and the illumination
optical system.
[0274] As illustrated in FIGS. 23 and 24, it is the outgoing
surface 132b of the optical prism 132 that functions as the
outgoing surface of the illumination optical system, so that the
cover 135 is formed such that also at the outgoing aperture portion
of the illumination optical system of the camera, only this portion
is exposed to the outside of the camera. Thus, the size, with
respect to the vertical direction of the camera, of the outgoing
aperture portion of the illumination optical system can be made
such that it looks the smallest, and the characteristic features of
the present embodiment can be utilized best.
[0275] On the other hand, the reflection screen 134 is made of the
semi-circular tube portion 134a and the semi-elliptical portion
134b, and the border between the semi-circular tube portion 134a
and the semi-elliptical portion 134b is at a position that
substantially matches the position in the axial direction that
corresponds to the light source center. The reason for this is that
if the position of the border at which the shape of the reflection
screen 134 changes is further to the front of the apparatus than
the light source, then a portion of the light rays reflected at the
semi-circular tube portion 134a is returned to the rear of the
apparatus behind the light source, so that the light rays emitted
from the light source cannot be condensed with high efficiency.
[0276] Moreover, if the position of the border is arranged further
to the rear of the apparatus than the position corresponding to the
light source center, so that the light rays reflected by the
reflection screen 134 do not interfere with the flashlight
discharge tube 133 and the cylindrical lens 131, then the
reflection screen 134 becomes very large with regard to the optical
axis direction, and miniaturization of the illumination optical
apparatus, which is one of the objects of the present embodiment,
is not attained.
[0277] For these reasons, it is preferable with regard to the
condensing efficiency and the size of the illumination optical
system that the position of the border in the reflection screen 134
substantially matches the position corresponding to the light
source center.
[0278] The following is an explanation of the ideal shape of the
optical prism 132. First, the ideal shape of the dimensions in
vertical direction of the illumination optical system is
explained.
[0279] In FIG. 20, it is preferable that the aperture height D of
the outgoing surface 132b of the optical prism 132 is within the
range of the Expression (5) below. That is, the ratio between the
aperture height D of the outgoing surface 132b of the optical prism
132 and the aperture height A of the reflection surfaces 134b and
134b' of the reflection screen 134 is given by:
0.4.ltoreq.D/A.ltoreq.0.8 (5)
[0280] In order to adapt to new camera designs, it would be ideal
to make the aperture height D as small as possible, but depending
on the size (aperture) of the flashlight discharge tube 133 serving
as the light source, the light loss becomes larger as the aperture
height D becomes smaller, and it may not be possible to configure
an effective condensing optical system.
[0281] That is to say, if the aperture height D of the outgoing
surface 132b in the vertical direction of the apparatus is reduced,
and the size of the light source (diameter of the flashlight
discharge tube 133) is increased, the light rays that travel
directly to the outgoing surface 132b of the optical prism 132 are
reduced. Thus, most of the components that would have been emitted
from the outgoing surface 132b are emitted from other portions of
the optical prism 132, and those components of the light rays
emitted from the light source that can be used effectively for the
illumination of the object are decreased. Consequently, with the
above structure, even though the aperture height D in the vertical
direction of the apparatus can be reduced, it is still not
necessarily an ideal illumination optical system with regard to the
effective utilization of light rays emitted from the light
source.
[0282] With regard to this, the lower limit of Expression (5) is
the aperture height D that functions effectively as the
illumination optical system, if the diameter of the flashlight
discharge tube 133 serving as the light source is relatively small.
And the smaller the diameter of the flashlight discharge tube 133
is in the expression, the smaller the aperture height D can be
made. However, due to such reasons as the durability and the
manufacturing process of the actual flashlight discharge tube 133,
there are no flashlight discharge tubes 133 below a certain
diameter.
[0283] Considering the inner diameter of flashlight discharge tubes
133 that can be manufactured in practice, then a lower limit for
the aperture ratio (D/A) of 0.4 seems appropriate.
[0284] On the other hand, if the upper limit 0.8 for the aperture
ratio in Expression (5) is exceeded, then the aperture height D
becomes large, which is not desirable with regard to the object of
the present embodiment, namely to reduce the size of the outgoing
aperture portion of the flashlight emitting apparatus in the
vertical direction of the apparatus.
[0285] The following is a discussion of actual numbers for
Expression (5) in a flashlight emitting apparatus according to the
present embodiment. In the present embodiment, the diameter (inner
diameter) of the flashlight discharge tube 133 is .phi.1.0 mm, the
maximum height A of the total reflection surfaces 134d and 134d' of
the reflection screen 134 is 5.6 mm, and the aperture height D of
the outgoing surface 132b of the optical prism 132 is 3.8 mm. From
these numbers, it follows that the value of the aperture ratio of
Expression (5) is 0.68, which falls into the range of Expression
(5).
[0286] The following is an explanation of the positional relation
in the axial direction of the illumination optical system. When L
is the distance between the outgoing surface of the reflection
screen 134 (tips of the reflection screen 134) and the ingoing
surface 132a of the optical prism 132, and B is the distance
between the outgoing surface 134 and the focus point O as shown in
FIG. 22, then it is preferable that the ratio of the distance L and
the distance B satisfies the following Expression (6):
0.ltoreq.L/B.ltoreq.1.0 (6)
[0287] With regard to making the illumination optical system small,
the distance L is ideally as short as possible. However, a certain
length (L) is necessary in order to make the aperture height D of
the outgoing surface 132b of the optical prism 132 narrow.
[0288] In the present embodiment, considering these aspects, the
distance L and the distance B are set such that the Expression (6)
is satisfied.
[0289] The lower limit 0 in Expression (4) means the state when the
reflection screen 134 and the optical prism 132 are in contact, and
this lower limit cannot be undercut. On the other hand, the upper
limit is set to 1.0, because when a larger value is taken, then the
illumination optical system becomes large in the optical axis
direction, and the goal of making the illumination optical system
smaller, which is one of the results of the present embodiment, is
missed. Moreover, when the distance between the reflection screen
134 and the optical prism 132 is L/B >1.0, then the light rays
directed toward the central region of the outgoing surface 132b
become very few, and preferable light distribution characteristics
is not likely to be obtained.
[0290] The following is a discussion of actual numbers for
Expression (6) in a flashlight emitting apparatus according to the
present embodiment. In the present embodiment, the distance L
(maximum distance between the reflection screen 134 and the optical
prism 132) is 4.4 mm and the distance B is 5 mm. From these
numbers, it follows that L/B is 0.88, which is within the range of
Expression (6).
[0291] In the present embodiment, the ingoing surface 132a of the
optical prism 132 is planar, and the outgoing surface of the 132b
of the optical prism 132 is concave, but there is no limitation to
these surface structures, and the ingoing surface 132a may also be
a convex or a concave surface. Here, by making the ingoing surface
132a a concave surface, there is the advantage that it is possible
to soften the refractive power of the concave surface of the
outgoing surface 132b, making it possible to avoid a concave lens
with a large drop of the outgoing surface 132b, but on the other
hand there is the disadvantage that the outgoing surface 132b is
broadened. In any case, the optical prism 13.2 needs to be
configured such that the outgoing surface 132b is a concave
surface, and that the overall optical prism 132 has a negative
refractive power.
[0292] With the above structure, it is possible to realize an
illumination apparatus in which the outgoing aperture portion in
the vertical direction of the apparatus can be made small, without
making the reflective screen 134 constituting the illumination
optical system unnecessarily large. Moreover, the above-described
structure does not compromise the changing of the irradiation angle
range, so that the irradiation angle range can be changed with
relatively high efficiency.
[0293] Referring to the cross-sectional view shown in FIG. 25, the
following is an explanation of the shape of the flashlight emitting
apparatus with regard to the axial direction of the flashlight
discharge tube. It should be noted that in this drawing, the same
numerals are given to members corresponding to those explained for
FIGS. 20 to 24.
[0294] A characteristic feature of the shape of the optical prism
132 is that its lateral sides in longitudinal direction are
provided with total reflection surfaces 132e and 132e'. Thus, those
light rays emitted from the light source that deviate from the
necessary irradiation angle range can be guided into the necessary
irradiation angle range, and the light from the light source is
utilized effectively. Another characteristic feature of the shape
of the outgoing surface side of the second optical prism 132 is
that its two end faces in longitudinal direction are provided with
slanted surfaces 132f and 132f'. Thus, it can be repressed that
light rays that are directed within the necessary irradiation angle
range escape at the two ends of the outgoing surface 1b, and the
distracting sensation at the seam with the cover 135 of the camera
body 26 can be eliminated.
[0295] On the other hand, a cylindrical lens with negative
refractive power is formed over the entire central region in
longitudinal direction of the outgoing surface 132b. Thus, the
condensing effect in the radial direction of the flashlight
discharge tube 134 is not adversely affected. By making the
outgoing surface 132b of a cylindrical lens with a single concave
surface, there is also the advantage that the camera can be
provided with a clear-cut appearance without distracting
features.
[0296] In this embodiment, an example of an illumination optical
system was shown in which the light rays emitted from the light
source center are condensed/diverged and the irradiation angle is
changed by the interaction of the reflection screen 134, the
cylindrical lens 131, and the optical prism 132. However, the
structure of the flashlight emitting apparatus of the present
invention is not limited to the structure of the flashlight
emitting apparatus described in the present embodiment. For
example, in the present embodiment, a concave cylindrical lens is
used for the outgoing surface 132b of the optical prism 132, but it
is also possible to configure this outgoing surface 132b with a
toric lens surface having also a refractive power in the axial
direction of the flashlight discharge tube 133 or a Fresnel lens
having negative refractive power.
[0297] Embodiment 5
[0298] Referring to FIGS. 27 to 29, the following is a description
of a flashlight emitting apparatus (illumination apparatus)
according to Embodiment 5 of the present invention. The flashlight
emitting apparatus of this embodiment is of the type in which the
irradiation angle can be varied.
[0299] FIGS. 28 and 29 are cross-sectional views of the flashlight
emitting apparatus, along the radial direction of the flashlight
discharge tube, in which ray tracing of the light emitted from the
light source center has been added. FIG. 27 is a diagram
illustrating the shape of the condensing optical system.
[0300] In the flashlight emitting apparatus of this embodiment, the
optical prisms made of acrylic resin or the like (that is, the
first optical prism 101 in Embodiment 3 or the cylindrical lens 131
in Embodiment 4) that were used in Embodiments 3 and 4 to condense
the light rays emitted from the light source on substantially one
point (the focus point) are removed, and instead of these optical
prisms, a reflection screen is used that has substantially
equivalent optical characteristics as the optical prisms. In the
present embodiment, the light rays emitted from the light source
are condensed on the focus point using only the reflection screen,
so that strictly speaking, not all of the light rays emitted from
the light source center can be condensed/diverged with high
efficiency.
[0301] However, since in the present embodiment the above-noted
optical prisms have been removed, there are the advantages that the
number of components can be reduced, and a cheaper structure
becomes possible. Moreover, as noted below, since the light rays
emitted from the light source are emitted out of the apparatus
after being condensed toward the optical axis, there is the
advantage that the outgoing aperture portion of the flashlight
emitting apparatus can be made small with regard to the vertical
direction of the apparatus.
[0302] Referring to FIGS. 27 to 29, the following is a more
detailed description of a method for setting the most suitable
shape of the illumination optical system of this embodiment.
[0303] In FIGS. 28 and 29, numeral 142 denotes an optical prism
having negative refractive power that is arranged on the outgoing
surface side of the illumination optical system, and that is made
of a glass material or optical resin material with high
transmittivity such as acrylic resin. Numeral 143 denotes a
straight tube-shaped flashlight discharge tube (xenon tube) that
emits flashlight when a trigger signal is input into it. Numeral
144 denotes a reflection screen (reflection portion) that reflects
to the emission side (to the front of the apparatus) those
components of the light rays emitted from the flashlight discharge
tube 143 that have been emitted to the rear and to the top or
bottom of the apparatus. The inner side (reflection surface) of
this reflection screen 144 is made of a metallic material having
high reflectivity, such as brilliance aluminum or the like.
[0304] Here, as shown in FIG. 27, the reflection screen 144 has an
elliptical surface with the light source center as one of the foci,
and reflects light emitted from the light source center and
condenses it to the focus point O which is the other focus of the
ellipse. The flashlight discharge tube 143 and the reflection
screen 144 are held integrally in a state in which the flashlight
discharge tube 143 matches the focus position of the elliptic
surface of the reflection screen 144. The unit made of the
flashlight discharge tube 143 and the reflection screen 144
(condensing optical system) can be moved in the optical axis
direction, and its spacing to the optical prism 142 arranged on the
outgoing surface side of the illumination optical system can be
changed. In this manner, the irradiation angle of the illumination
optical system can be changed continuously by changing the distance
between this unit and the optical prism 142.
[0305] In the present embodiment, an aspect that is different to
Embodiments 3 and 4 is that, although not shown in the drawings,
those light rays emitted from the flashlight discharge tube 143
that are not reflected by the reflection screen 144 but travel
directly toward the optical prism 142 are not condensed on the
focus point O. Moreover, the light rays emitted from the flashlight
discharge tube 143 that are directed toward the rear of the
apparatus are reflected by the reflection screen 144 and return to
the flashlight discharge tube 143. Here, the reflection surface of
the reflection screen 144 is formed as an elliptical surface, as
described above, so that different to the foregoing embodiments,
the light rays reflected by the reflection screen 144 are all
directed in a direction away from the light source center.
Moreover, strictly speaking there is refraction at the glass
surface of the flashlight discharge tube 143, and the light rays
cannot be condensed on the focus point O and are somewhat
broadened.
[0306] To facilitate explanations, FIGS. 27 to 29 illustrate the
ray tracing without showing the influence of the refractions at the
flashlight discharge tube 143. It should be noted that it is
possible to consider the influence of the refractions at the
flashlight discharge tube 143 (glass tube) and to correct the shape
of the reflection screen 144 to a suitable shape. This way, the
light rays that are emitted from the light source toward the rear
of the apparatus can be reflected by the reflection screen 144 and
condensed on the focus point O.
[0307] As shown in FIG. 28 and 29, in the flashlight emitting
apparatus of this embodiment, as in the foregoing embodiment, the
outgoing surface (negative lens portion) 142b of the optical prism
142 is devised as a concave surface (having negative refractive
power). Moreover, the ingoing surface 142a of the optical prism 142
is formed as a planar surface. Thus, with regard to the positional
relation of the illumination optical system as shown in FIG. 28,
the light rays from the condensing optical system are refracted by
the ingoing surface 142a, and are emitted to the outside of the
apparatus after passing through the entire outgoing surface 142b,
and the irradiation angle range of the illumination light can be
made narrow. Moreover, with the positional relation of the
illumination optical system as shown in FIG. 29, the light rays
from the condensing optical system are refracted by the ingoing
surface 142a, and are emitted to the outside of the apparatus after
passing through the central region of the outgoing surface 142b
near the optical axis, and the irradiation angle range of the
illumination light can be broadened.
[0308] Moreover, the outgoing surface 142b of the optical prism 142
can be made very small in the vertical direction of the apparatus
with the aperture of the reflection screen 144, and the size of the
outgoing aperture portion of the flashlight emitting apparatus in
the vertical direction of the camera that is apparent from outside
the camera can be made very small, as in Embodiments 3 and 4.
[0309] With the above-described structure, it is possible to
realize a flashlight emitting apparatus in which the outgoing
aperture portion is made small with regard to the vertical
direction of the apparatus, while reducing the number of optical
elements constituting the illumination optical system. Moreover,
also the structure of this embodiment does not compromise the
changing of the irradiation angle range, so that the irradiation
angle can be changed with relatively high efficiency.
[0310] In the present embodiment, an illumination optical system
was shown in which the light rays emitted from the light source
center can be condensed and diverged with two members, namely the
reflection screen 144 and the optical prism 142. However, the
present invention is not limited to the shape of the illumination
optical system of the present embodiment. For example, in the
present embodiment, the outgoing surface 142b of the optical prism
142 was configured as a concave cylindrical lens, but the outgoing
surface may also be configured as a Fresnel lens. Moreover, the
outgoing surface 142b may also be configured as a toric lens
surface having also a refractive power in the axial direction of
the flashlight discharge tube 143.
* * * * *